Per the IGC GNSS specs

2.5.4. Date of flight - the date used in the file name and in the H-
record (DTE code) is the UTC date of the
first valid fix in the flight log transferred after flight. That is,
the date applicable to the time in the first line
in the B (fix) record, not the date at the time of switching on, or of
take-off. This is particularly important
for recorders operated in time zones where they are switched on close
to midnight UTC. (AL6)

Therefore, one would conclude that there must be some fix form the 8th
on the log. But, interestingly the "B" records (flight gps fix points)
only have UTC Time in them.

So the question would be: Did you power up your 302 on the 8th?
(maybe, just to do a new flight declaration)

Also, is there a big gap in the first few "B" record times? (i.e. a
few points from the 8th followed by times from the 12th)

"B" record format (in part)
B H H M M S S D D M MM MM N D D D M MM MM E V P P P P P G G G G G CR
LF
Time UTC 6 bytes HHMMSS
Latitude 8 bytes DDMMmmmN/S
Longitude 9 bytes DDDMMmmmE/W

Or, for you conspiracy theorists: This is a result of some secret
military test on the GPS system meant to test for gaps in the space
time continuum ;-)