Lost Route Points after edit

Possibly a problem within the gpx file itself.

What you could do is duplicate (note not copy) the route and then make the necessary adjustments to one of them, any differences will be visible allowing you to make any necessary changes so that it follows the original.

I have seen this type of Basecamp route point "thinning" of imported basic gpx routes of only 15 points (Stops).

I have also seen "successful" importation of a similar 3rd party gpx route with over 100 points directly into the Nuvi 56. The Nuvi with trip planner split the 800 mile route into 5 separate trips of fewer than 29 points, while retaining an excess of neighborhood street turn points in some instances. So it may be that if the route is imported directly into a Nuvi, automatically recalculated, and then exported from the Nuvi to Basecamp in a Garmin Current.gpx file that editing on the computer may give more satisfactory results.

Note: I did not follow up on all the ways that Basecamp might lose a few route points on imported routes, but one in_line highway point (Stop) seemed to be thinned just because B/C considered it redundant in a manner similar to track log point thinning on straight roads. Perhaps it was a result of where the mouse pointer was located along the route in the computer when a recalculation was performed. It may also be that the B/C non-digital waypoint number sorting and reordering loses a few route points if more than 9 points are present and editing and recalculation has occurred.

Route 66 GDB data

Thanks for your comments. I was lucky enough to find a zipped file od Route 66 data by James McCool (on http://www.historic66.com/gps/garmin).
This is a masterpiece (dated 2007) with 8 gdb files (1 for each state). Each one contains a "Main Route" which maximises use of the original sections plus numerous other dead ends and isolated sections which still exist. There are a few instances when the "Main Route" actually loops off at an Interstate junction to follow a few miles on the parallel R66 pavement only to loop back at the next junction. It was these short diversions that I was trying to edit out when I encountered the problem of lost data. I am now getting round this by converting the "Routes" to "Tracks" which can be freely edited. These will be loaded on my 8" screen Android Tablet (using Osmand SW and OSM maps) for the road trip. It would have been nice to have and Android version of Basecamp to use, but a lot of people are still waiting!

We seem to be on different wavelengths here. I did download and review your above "historical 66" link yesterday in its original format, but thought that too many of the larger cities as well as other areas had been bypassed with Interstate Highway routing to keep the quantity of "Vias" at a minimum. Therefore I would have added to, not subtracted from his shaping points. If you stay on the interstates, you really won't need much in the way of gps devices and maps, but will see the more of the country whiz by at a faster rate.

R66 Routing

Sorry if I did not explain myself. I'm certainly trying to avoid Interstates wherever possible. There are however a few short loops of R66 which when examined with Google Earth do not have anything of interest along then. For instance on the Illinois section there is a 2m stretch of R66 (adjacent Burr Ridge) which probably involves a further 2m of I55 junction loops to get off and then back onto I55 (with all the risks of making a wrong turn). As this James McCool routing is the best I've found so far It'll do us just fine (with a few minor tweaks)

Thanks for your comments. I was lucky enough to find a zipped file od Route 66 data by James McCool (on http://www.historic66.com/gps/garmin).
This is a masterpiece (dated 2007) with 8 gdb files (1 for each state). Each one contains a "Main Route" which maximises use of the original sections plus numerous other dead ends and isolated sections which still exist. There are a few instances when the "Main Route" actually loops off at an Interstate junction to follow a few miles on the parallel R66 pavement only to loop back at the next junction. It was these short diversions that I was trying to edit out when I encountered the problem of lost data. I am now getting round this by converting the "Routes" to "Tracks" which can be freely edited. These will be loaded on my 8" screen Android Tablet (using Osmand SW and OSM maps) for the road trip. It would have been nice to have and Android version of Basecamp to use, but a lot of people are still waiting!

The URL link above includes this comment about Mapsource circa 2007. In my limited experience, Basecamp circa 2014/2015 may have a similar design:

"How to use these files:

After downloading the files, save them to your Garmin Mapsource custom route folder. You can then transfer them to your GPS unit via the USB interface once you open the Mapsource program. Depending on the capacity of your particular GPS unit, you may or may not be able to load all eight files at once.

Each state file is broken down into several parts. These parts consist of different, optional alignments of Route 66. They are listed numerically first, 1-9, then after the number 9 I had to label routes alphabetically A-Z because the software would not acknowledge the numbers 10 and up as being after the number 9 (e.g. it would put 10 before 2). Don't worry, it really is not confusing."