Spectracom driver should handle GPS rollover

The Spectracom driver does not handle GPS rollover. I wish it did, as my GPS clock has rolled over and is outputting 99 for the year:

$ date --utc
Sat Jan 12 08:07:47 UTC 2019
$ cat /dev/spectracom0
  99 149 08:07:48.001  S

That is the 149th day of 1999. If you add 1024 weeks to that, you get the correct date, so this is obviously GPS rollover.

The NMEA driver has some code to deal with GPS rollover, but I don't fully understand how it works, so I'm not sure if that's directly usable in this situation.

Alternatively: in practice, I don't much care about the GPS time. I really only care about the PPS. Is there a way to use the PPS with network sources? In other words, can ntpd be configured to use network sources to get the time as per normal, and then use the PPS to tighten up the precision on the start of the second? I've split this idea out into #538 (closed).