From what I’ve heard its to confirm that the record has been inspected. What do all the numbers mean? If it is for inspection, why doesn’t it simply say, “ok” then a short operator’s number?
If its not an inspection number what is it?
I noticed most (if not all) are hand scratched into the record. If its worth all that effort its gotta mean something useful.
I’ve been meaning to talk about this for sometime, though it doesn’t answer the O.P. Go check out your old Eagles albums and read what’s etched there.
It has nothing to do with inspection. It’s the record’s matrix number, essentially a serial number identifying the master from which the record is produced. Usually there’s something to identify the number of the record side. Occasionally there is also a message identifying the mastering studio and/or the cutting engineer (“A Porky prime cut!”), and sometimes there are “secret” messages added.
Or your old Joe Walsh albums. Y? Because we like U. 
Eagles? Joe Walsh? Pish posh. My collection of 78s includes:
Duke Ellington “Mood to Be Wooed” 20-167OB 11 S
Benny Goodman Sextet "Ain’t Misbehavin’’ cc35206
Woody Herman “No Greater Love” HCO 2219
Benny Goodman and his Orchestra “My Blue Heaven” co 3673 9
Lionel Hampton “Slide, Hamp, Slide” L 4008 AD
No secret messages that I can detect. I’d have to go with Biffy, that they relate to the master used.
I’ve started a new thread in Cafe Society in case anyone wants to post the messages found on their LPs.
(Man, the hamsters are slow today!)
If its not for inspection reasons, why is it hand scratched (or am I just misunderstanding it and they are machine etched)?
They are “hand scratched”, but not on every single record. As I understand it, the etching is on the master disc, which is used to make the vinyl discs.
They’re stamped into the vinyl, just the same as the grooves.