On Dec. 24 I spent 3-4 hours cruising the warren of little streets nearby with my GPS. For fear of exceeding some server limit on uploaded points, I broke my tracking into three segments. After the first two, I saved the track under a name, then cleared the track log. I saved the third segment but did not clear the log. I found the first two segments failed to upload to OSM for lack of timestamps.
Examining the GPX files, I found my three named track, all three missing timestamps. At the end of the file I found a track named ACTIVE LOG which retained its timestamps. This explains a couple of things, in particular, why I keep getting messages about points not loading due to missing timestamps while the tracks do show up on OSM. Basically saved tracks are redundant to the log, and that is all that needs to be uploaded. Corollary: it should not be cleared until I've captured it as a .gpx file.
The original logs may be available on my data card -- the file with a date-derived name shows up with others there. Trouble is, I don't know how to get at it. The basic Garmin driver doesn't seem to give access to the card as USB storage.