GPS units, like most other Garmins would take up to 1000 waypoints. But some units seem to limit users to say 100 waypoints.

Here is a workaround you can try:

Take your collection of waypoints in BASECAMP and export it as a GPX file. Then copy this GPX file (give it a userfriendly name) to the GPS. Place it under Garmin/GPX/ folder.

You should see several other GPX files in this location. The one called current.gpx is the tracks that currently display on the device.

There may also be an Archive folder under /GPX/. In here the GPS will store archived track logs, handy if you need to get it in future. Note that GPS stores only 10k track points in current/gpx and then it will archive.