Does anyone have a good regular expression that will match all legal LC 
Call Numbers from the LC Classified Schedule, but will generally not 
match things that could not possibly be an LC Call Number from the LC 
Classified Schedule?

In particular, I need it to NOT match an "MLC" call number, which is an 
LC assigned call number that shows up in an 050 with no way to 
distinguish based on indicators, but isn't actually from the LC 
Schedules.  Here's an example of an "MLC" call number:

"MLCS 83/5180 (P)"

Hmm, maybe all MLC call numbers begin with MLC, okay I guess I can 
exclude them just like that. But it looks like there are also OTHER 
things that can show up in the 050 but aren't actually from the 
classified schedule, the OCLC documentation even contains an example of 
"Microfilm 19072 E".

What a mess, huh?  So, yeah, regex anyone?

[You can probably guess why I care if it's from the LC Classified 
Schedule or not].