I am using Basecamp 4.6.2 with Windows 10. After transferring 580 waypoints from Basecamp to my Nuvi 2598, I took a trip and added three new waypoints. Then I connected the Nuvi to my computer and opened Basecamp. All 583 waypoints have the same creation and modification date listed in Basecamp; namely the current computer date and time. Therefore a time sort to find the three new waypoints is useless. The "Date Created" and "Date Modified" columns are meaningless.
The waypoint symbol is also a problem. Any waypoint copied from Basecamp to the Nuvi and then back to basecamp from the Nuvi has its symbol changed in Basecamp.
In other words, Garmin software (Basecamp) and hardware (Nuvi 2598 and also my Oregon 450t) handle waypoint dates and symbols very poorly. Basecamp and its predecessor Mapsource have lots of nice features. But the lack of coordination between Garmin hardware and software is a serious problem that Garmin should quickly addresses.