Prior to 1 January 2000, the so-called Y2K had everyone on edge about what would happen when the year rolled from 99 to 00 on devices with only two digits to note the year. There was significant preparation and work (and a lot of snake oil sold, imho), but it ended up being a pretty smooth transition and using four digits (instead of two) is now the norm. Not sure what will happen on 31 December 9999 but, honestly, that’s not really going to be my problem.
All of that said though, it seems that GPS may have a similar issue on 6 April 2019. According to this article, GPS signals from satellites include a ten binary bit timestamp, allowing for a maximum of 1,024 weeks (roughly 20 years). When that number rolls (from 1,023 to zero), if the GPS unit isn’t patched to accommodate for it, the GPS may not be able to calculate position or data could be corrupted.
According to the article, most standards compliant GPS systems that have been manufactured since 2010 should be fine. If you have a GPS system (or, perhaps equipment to track trucks, boats, planes, etc.) that is older than 2010 or is not update-able (e.g., was purchased out of the back of a van in an underground parking lot somewhere from a dude wearing a trenchcoat….), there is a chance that it will stop working (or stop working right) on 6 April 2019. If you’re unsure of the details on your device and you aren’t able to get in touch with the manufacturer, any GPS devices legal for use in the US should have an FCC ID. You can look up the FCC ID here and get most of the information.