Sometimes this month, I believe, that the notification icon at the very top of MATE morphed from a bell into a mailbox.
I have 2 machines: one that I upgraded from 18.x to 19.10 and another one which I installed 19.10 after wiping. Both are always running latest patches and updates.
Not only are those 2 systems behaving somewhat differently as I started explaining here: /usr/bin/variety stopped working due to new clock/time format? but not so long ago (Possibly last week?) I also noticed that this system that was upgraded from 18.x was still showing up the old bell icon. Of course, I logged off (and also had to reboot) before posting this so I am CERTAIN there is a discrepancy in terms of what is deployed/displayed on my systems now and I again wanted to raise a flag in case I wasn't the only person getting this result?