The ideal number of records in the stack will depend on the thickness of the records. Some of the older LPs are quite thick compared to the almost flexible plastic used later. The amount of weight will also affect how much the bottom records label gets scratched as the umbrella on the spindle retracts. The only real limit on a Lab 80 would be the length of the spindle above the umbrella and the ability of the arm and stylus to be able to clear the top record when all have dropped.
Every changer has a variation of this problem. We had a table top Zenith Cobra where the spindle is split at the bottom of the stack. A pin rotates 180 degrees to pull the bottom record to align with the lower spindle. Terrible wear, especially with a load of 78s. Over time, it also developed the bad habit of dropping a record, starting the play, then somehow dropping the entire stack on top of the arm.