A member of the EFS-Web listserv posted this question to the listserv earlier today:
His question is a very interesting question. Here is the answer.
In the old days, most patent applications were paper-filed rather than e-filed, and for the e-filings, USPTO assigned application numbers to the various e-filing processing workflows in blocks of 1000.
So a block of 1000 numbers would be given to the e-filed 371 cases (entries into the US national phase). And a block of 1000 numbers would be given to the e-filed 111a cases (continuations, divisionals, new domestic applications). Other than those two blocks, all of the numbers were allocated to the mail room where paper-filed cases where handled. It would take months or a year to use up a block of numbers for any of the e-filing workflows in those old days because e-filing was rare.
Nowadays of course the rare activity is the paper filings. About 98% of patent applications in USPTO are now e-filed.
But the distribution of work between the two e-filed workflows (371 and 111a) is extremely asymmetric. There are half a million 111a cases filed per year. In contrast there are only about 35K 371 cases filed per year.
I think nowadays the application numbers are probably assigned in blocks of 10K. This would mean that the 111a workflow uses up a block per week. In contrast the 371 workflow takes four or five months to use up a block.
So at any given instant, the block of numbers in current use for 371 cases is anywhere from a month to five months older than the block of numbers in current use for 111a cases.
So it is no surprise at all that a person could file a 371 case and a 111a case on the same day, and the application number given to the 371 case would be a much smaller number than the number given to the 111a case. For example one day in July we filed a 111a case and the application number that EFS-Web gave to us was 15/219,xxx and on the same day we filed a 371 case and the application number that EFS-Web gave to us was 15/114,xxx.
Similarly it is no surprise that your new 371 case application could have a number that is much smaller than the number you received a couple of months ago on a 111a case.