How does the USPTO handle facsimile transmissions for dating purposes?

The USPTO has specific rules for dating facsimile transmissions. According to 37 CFR 1.6(a)(3):

Correspondence transmitted by facsimile to the Patent and Trademark Office will be stamped with the date on which the complete transmission is received in the Patent and Trademark Office unless that date is a Saturday, Sunday, or Federal holiday within the District of Columbia, in which case the date stamped will be the next succeeding day which is not a Saturday, Sunday, or Federal holiday within the District of Columbia.

This means that faxed correspondence is generally dated on the day of complete transmission, except for weekends and holidays, where it’s dated the next business day.