GPS provides the time (hour, minute, seconds) and date (day, month, year) over the NMEA messages. It also provides a week counter. This wraps around at 1024. The last time was about year 1999.

With most of the things I have used NMEA for (time sync), I did not use the weeks counter. However if there is any software that does use it, it needs to be able to handle the rollover.