Am I wrong in deducing that the 665 moves the route data from the SD card to the native storage when it imports the route?
Wow, so is the updated 5xx series of motorcycle navigators saddled with the same severe storage limitations? Wish I would have known before I bought this one.
Not sure what you mean by severe storage limitations. You may need a card for future map updates, but no different to cameras, phones etc that require memory cards.
Probably, but some information is likely stored on the device (perhaps route title and a pointer to the location on the sd card). In addition, the route may well be loaded on the device when active.
How much memory is available on the device when viewed thru windows as an external drive? (i.e. not thru basecamp)
How many routes are on the device/sd card?
How many trip logs have been saved?
How may total points in the route that gives the memory error? (export the route as gpx and open it with excel)
All devices have limits on the number of routes, waypoints etc. allowed. In addition, there are limits on the maximum number of user points allowed in a route, the number of total points in a track and I suspect the total number of points in a route (this would include the path between user points). These all vary by device. As far as I know, all devices log data to the device memory only - nothing is written to an sd card.
Typically the design of the device will have reserved enough device memory to handle these limits. So, even if you could store 1000 routes on an sd card, the device itself will not have enough reserved memory to store the information needed for retrieval or listing the routes.