Can the terms “serial number” and “application number” be used interchangeably? The answer is “no” as I will discuss.
“Serial” means “a thing composed of numerical digits that increments one at a time”. So by definition if a thing that we are discussing has stuff in it that is not numerical digits, it cannot properly be termed a “serial number”. You can see a discussion of this in Wikipedia.
So for example “PCT/US2017/12345” is not a serial number. It has virgules and letters in it.
But for the same reason, “15/123,456” is not a serial number. It has a virgule in it. And the first two characters are not really an incrementing integer.
There are at least two reasons why the series code is not really an incrementing integer. The first reason is that “000,000” is not a valid serial number at the USPTO. Even if a series code increments (as has often happened, for example 14 was succeeded by 15) the overall progression is not a serial progression. 14/999,999 was followed by 15/000,001 which is a jump of two counts.
A second reason is that the series code does not always increment. When the USPTO runs out of “78” application numbers for trademarks, they will not increment to “79”. The series code will jump to “80”.
So the text string that includes a series code and a virgule is not a serial number at all. It can only be termed an application number. The MPEP spells this out. An application number, the MPEP explains, is defined as a two-digit “series code” and a virgule and a six-digit serial number. (For purposes of this discussion the comma that might appear between the third and fourth digit of the serial number is to be ignored. The comma does not disqualify the six digits from being called “serial”.)
In the old days at the USPTO, it would take five years or even ten years to use up a block of (one million) serial numbers. And the number of cases that remained pending for so long that a duplicate serial number could give rise to possible ambiguity was vanishingly small. So in the old days, nobody inside or outside of the USPTO worried about any need to recite more characters than just the serial number when referring to a particular application.
In the old days, the USPTO used the color of the physical patent file folder to denote the series code. So if there happened to be two (physical) patent file folders with the same serial number, it would be instantly evident which one was which simply by looking at the color of the physical file folder. (It would also be instantly evident which one was which because one file folder would be new looking and the other would be frayed around the edges and corners and would be faded in color due to a decade of exposure to harsh fluorescent light.)
Which then brings us to the strained and uncomfortable change in the TMEP that the Trademark Office made about six years ago.
If you go back more than about six years, the TMEP said exactly the same thing as the MPEP. An application number was defined as a two-character series code and a virgule and a six-digit application number. It had been that way for decades for trademark applications, just as it had been that way for decades for patent applications.
Then about seven years ago, I ticked off the Trademark Office. I filed an application for a sound mark. The TMEP explained exactly how the practitioner is supposed to email the “drawing” (the audio WAV file) and the “specimen” (also an audio WAV file) to particular email addresses at the USPTO. (Back then, TEAS did not have any mechanism for uploading media files as part of a trademark application, which is why email had to be employed.) The TMEP said that the email should mention the “serial number” and the TMEP did not require the practitioner to provide the “application number” as part of the email communicating the audio file.
Back when that section of the TMEP was written, which was maybe 1990, there was never more than one active series code for trademark applications. It was 73 or 74 or 75 but there was only one active series code at any given moment in time.
By the time of my story, however (the year 2010), there were three active series codes. There was 76 for applications filed in legacy fashion (on paper) and there was 78 for e-filed applications, and there was 79 for Madrid Protocol cases. This meant that any given serial number could conceivably be any of three pending applications — a paper-filed application, an e-filed application, or a Madrid-filed application.
The person at the USPTO who received my email pushed back. This person demanded that I provide the application number, not merely the serial number. I also pushed back, pointing to the TMEP that said I only had to provide the serial number. Eventually I “won” in the sense that the USPTO person gave up and inserted my audio file specimens into the file. (You can see the case here in TSDR.)
At which point a bunch of people at the Trademark Office must have gotten riled up. What if another practitioner some day were to stubbornly provide only a serial number instead of an application number? Clearly Something Would Have to Be Done.
They must have done a text search in the TMEP to see how many times “serial number” appeared in places where it probably would need to be updated to say “application number” (in view of the fact that the number of active series codes was nowadays three rather than one). And they found that there were maybe sixty places. Sixty places where a stubborn practitioner like me could supply a six-digit serial number and could refuse to provide the series code, and the USPTO employee would have no choice but to do the tedious work of looking in two or even three application files to figure out which of three applications the communication might refer to.
The correct next step at the Trademark Office would, of course, have been to revise the TMEP so that most of the places that said “serial number” would be revised to say “application number”. There would be a few places where the phrase “serial number” would have to be preserved. Probably it would require many meetings and conference calls to work out which of the places “serial number” should change and which of the places “serial number” should be preserved.
Rather than carry out the tedious work of actually revising the TMEP properly, somebody at the Trademark Office decided to do something very awkward. Somebody at the Trademark Office decided to amend the TMEP to redefine the term “serial number” to mean “the thing you get when you put the series code and a virgule in front of the serial number”. This is of course very self-referential and probably you end up being able to say that “76/76/76/123456” counts as a serial number. Sort of like the Escher print where the lizard is eating its own tail.
For the next practitioner after me, maybe in 2011 or 2012, who was emailing an audio file to the USPTO, this would mean that the practitioner should mention the series code in the email. The USPTO person could then bounce the email if it did not mention the series code.
It is of course nonsense for the term “serial number” to simultaneously mean “the thing with six digits” and “the thing you get when you put two more characters and a virgule in front of the serial number”. But that nonsense is exactly what appears in the TMEP to this day. As I say, when you read the new (very awkward) language, you get the impression that “76/76/76/123456” could count as a valid serial number.
So in the world of trademarks at the USPTO, the terms “application number” and “serial number” are supposedly interchangeable. But in the world of patents at the USPTO, the two terms are most definitely not interchangeable.
I remain stubborn about this even now in 2017. When I write a response to a trademark Office Action or otherwise mention a trademark application in an official document, I never call it a “serial number” unless it only contains six numerical digits. If it has a series code and a virgule, I never call it a “serial number”. I call it an “application number”.