garmin gps60 - 200km route truncated as i continue my trip

The problem here is that you are probably running out of Trackpoints, (Waypoints are single locations), you have about 10,000 Trackpoints (only 500 Waypoints), they are autoimatically generated as you travel and when the track log is full, your unit will either stop adding new trackpoints or delete early trackpoints in order to store new ones.

From the Main Menu select Tracks, there will be a Track log percentage figure showing how full the log is, now select Setup, the first item is 'Wrap when full' which I guess you has selected, below that is 'Record Method', and 'Interval', this should fix your problem, you can tell the GPS how often it should store a new Trackpoint, you have Auto, Time and Distance. If you select Distance and 0.05 Km, your GPS will store a new Trackpoint every 50 Metres, so after 200km you should have 4000 Trackpoints (about 40% full)

 

10,000 is the total for all tracks

 

Your friend's GPS may be able to store more Trackpoints than the GPS60 , or maybe several tracks have been joined together using Basecamp.

If you double click on a track in Basecamp, go to properties >> Index, you can display the number of Trackpoints in the track.

You can save a new track with less Trackpoints in it with :-

Right click on track >> Advanced >> Filter Selected Track >> Set Maximum Points >> Save Original Track