This is the situation I have with the bathroom silicone caulking.
The last time I did it was 8 years ago. Is it safe to conclude both a and b need to be removed b/c of bonding issues, as well as the caulking is likely done in one piece when done correctly?
Yes! Next time, find color matched caulk, and use the blue tape straight line above and below the caulk job. That way, you can push it in nice and tight, then simply pull the tape and you will see a nice, straight caulk line.