On Thursday, January 1, 2015 1:30:26 PM UTC+1, Tim Newport-Peace wrote:

Not quite.

The date is received as a 10-bit number from satellite transmission. The
GPS engine stores the epoch number. It is the epoch number which is lost
when the RTC battery discharges.

Epoch 0 ran from 6th Jan 1980 when GPS went active.
Epoch 1 (the current epoch) ran from 22nd Aug 1999.
Epoch 2 will begin on 7th April 2019.
Epoch 3 will begin on 21st November 2038
and so on.

Any fix needs to be ready for 7th April 2019 or we go back to page 1.

It would seem that Garmin introduced a temporary solution at in the
middle of 2000, causing all GPS OEM modules not to have a problem from
1996 to End of October 2014. This fix works correctly from 1.January
2005 +- 512 weeks, which has now expired. Hence the current rash of
problems.

Well I hoped that GPS Epoch changes are handled better by Garmin. So the fix that I suggested would work for about next 4 years until April 2019.

Do you remember what happened with GPS 25 module when the first GPS Epoch finished in 1999 ? Was it able to get proper position and time but it had wrong date, or it was not able to get the position at all ? If the former, it may be possible to create a revised 'dirty fix' that would work after April 2019