The square brackets at the front of the name are simply for my benefit so that it sorts correctly in a regular file browser. But I had hope that your solution would work.
I took your advice and moved the folder out of the Plex folder, renamed it to
Beatles for Sale (1964)
I did the Plex dance, moved the folder back, re-scanned library, and once again it says 1964 for like one second until it’s able to pull the data from the internet, at which point the album artwork spins around and the date changes to 2009. 
It’s also worth repeating that the same exact folder (and indeed, one that literally has 2009 in the title…
[1964] Beatles for Sale [2009 Mono Remaster]
…both display as 1964 in a test server I created this morning on my Mac, so it seems that it doesn’t care about the year in the folder name regarding music.
