As drossal pointed out above, the manual clearly states 250.
This screenshot shows a Legend Cx with several Routes loaded, some have 240 points and some 120 and none were truncated. (The second shot shows how many more routes were added before truncation occurred.)
The 50 point limit applies where the route is used in 'follow road' mode (this limit is mentioned in the manual too).
The problem is that the GPS can be set up in such a way that 'follow road' is not just the default but the only option - in that case yes your GPS is truely limited to 50 points per route and will throw error messages on longer routes like the ones pictured above.
[edit] agreed, 50 is way more than enough for any day ride, in 'follow road'.
But it's a setup thing, it doesn't have to be that way.
[edit] This seems to crop up so often, I've added a new how-to
page here.
It's OT with regard to the original query though, which is about truncation during the upload process - a different thing. A Route of more than 250, or a Track of more than 500, will truncate during upload, throwing a small error message on the GPS only (see r-h pic above), which may well get overlooked. Later when you try to follow it, the GPS won't show any error, but simply run out of points in the middle of nowhere.