A few questions about old vinyl records...

I just got through transferring 15 vinyl records for a client. These were all done in the late 1960's and early 1970's. My experience in learning to cut acetates dates from the late 1970's when I was interning in Nashville.

I have noticed some things about the 1960's-1970's records that I have some questions about.

One a lot of the records had low level 60 Hz hum on them. They also had some very low frequency "bumps" in the spectral display mostly around 20 Hz. The correlation on a lot of the tracks tends to be negative. Some records seem to be almost mono with very little separation while others show really wide panning. Some of they have very very wide groves other have groves that are almost touching, Did the lathes in the 1960's not have computers? The level from track to track seems very inconsistent. On a lot of them there is a large spike at 15,750 kHz which is the horizontal oscillator frequency from a B & W TV. Why??? These are almost all "vanity pressings" done by unknown record plants. I checked my turntable and phono preamp and it does not have any of these problems with more modern commercial records.

Just wondering??? Thanks in advance for any information...