During early stereo recordings, were there technical problems that caused records to continue to be released with mono tracks in different channels?

Answer 1

It's a bit of a technical issue and an economic one- Stereo vinyl mastering is more complex than mono, and there were limitations based on most listeners' adoption of stereo hifi systems at home.

Up until the mid 1950s, almost all consumer playback systems, and commercial vinyl mastering lathes, were mono only. Stereo records and hifi systems began to be available in the late 50s, but adoption took time. Consumers didn't want to part with their older systems quite yet, and engineers were still adapting to the added complexity of cutting masters in stereo.

This complexity is partly why early stereo records are often hard-panned- partially panning a signal (particularly bass and low frequency information) between the left and right channels can cause phase de-correlation between the left and right. If this phase de-correlation is exaggerated enough it can cause the needle to skip out of the groove. It took some time for vinyl mastering engineers and mix engineers to adapt their techniques to stereo.

The other part has to do with listeners, who still wanted to hear everything even with mono hifi systems. Hard panned records are "mono compatible", meaning if you sum the left and right channels into a mono signal there should be no destructive interference due to phase cancelation. So you can take a stereo record, make it mono, and nothing will be lost.

Records made after about 1965 are predominantly stereo, since almost all new turntables and amps of the era had become stereo, so more adventurous panning begins to be commonplace about this time.

Hope that helps!