Until now, we allocated all patents to a year by using a mix of the filing date and the earliest publication date.
For all priority applications and direct filings, we took the application filing date. However, this date is problematic for regional/national phase applications of a PCT. For these applications, offices artificially set the PCT filing date as the filing date of the regional/national application. In these cases, we take the first publication date instead of the filing date because it is much closer to the actual time when an attorney worked on prosecuting the application.
Still, when comparing our statistics to other databases, our users sometimes need one or the other. We added a “date switch” feature next to the year selection box. You can also switch to grant year now (of course, for granted patents only).
Our mixed date is still used for “Prosecution Year” and remains the standard selection because we believe it is the most correct one.