Is there a way to prevent the various tracks being mashed together?
Short answer: don’t know, however to ‘unmash’: ‘Divide’ (in Tools) the track into desired segments (after uploading to BaseCamp)
I use a 78, however, still have a 76, but haven’t used it in years.
I just plugged it in with BaseCamp active.
It has a number of ‘tracks’ on it (from 2017).
With tracks named like: ‘ACTIVE LOG nnn’ (where nnn increases)
There are no ‘tracks’ covering more than one day.
There are many separate tracks on the same day.
This goes with what you are saying.
In the 78, you manage tracks differently.
They all go into one track ‘Current Track’, and you can ‘Archive’, ‘Save’, etc.
I don’t use that functionality, I just ‘edit’ the ‘Current Track’ in BaseCamp.
I save all my tracks from daily paddles (for my ‘paddling log’). (even from long trips, last one in '09: http://www.yakabout.us/fska/Aus09_trk.htm)
What I do:
After my paddle, I upload the ‘Current Track’, then ‘trim’ it for my trip, then rename it to ‘yyyymmdd’ (sometimes with a suffix of ‘a’,‘b’, etc)
With your 76, you could do something similar, you will probably do a combination of using the ‘Divide’ and ‘Join’ functions under Tools, or the ‘right-click’ menu (join isn’t under ‘Tools’).
The way I do it, is I ‘open’ (double-click) the track, then manually remove all points not of interest (I go to the ‘date’ I paddled, find when the speed starts moving, remove the junk, before trip & after)