The first alpha in runouts (for all plants) indicates year of mastering (between 1960 and 1977): L=60, M=61, N=62, P=63, R=64, S=65, T=66, U=67, W=68, X=69, Z=70, A=71, B=72, C=73, D=74, E=75, F=76, G=77.
The 2nd alpha indicates size/speed; K=7" 45, L=7" 33⅓, P=10" 33⅓ & R=12" 33⅓.
"4" indicates lacquer cut from tape supplied & "5" indicates lacquer supplied to RCA. Either of these digits in front of the 2nd alpha = January to June and behind the alpha = July to December of the year indicator.
The 4th alpha indicates whether a record is mono ("M"), stereo ("S"), or even quadraphonic ("T").
(e.g. R4KM prefix would be a 1964 7" 45, cut between Jan & Jun from tape supplied)
A 1" diameter pressing ring seen on label are characteristic of RCA pressings from 1968-70 onwards), and 'RC' code within deadwax assist in identifying these pressings.
In the early to mid-1980's, RCA pressings of PolyGram sublabels were indicated by a '70' code on the center label, while pressings of releases on A&M Records bore an 'R' code on the label.