Okay, so I've alway been curious about vintage pack prices and contents and recently decidedly to delve deeper into '50s-'60s wax packs knowledge. Before 1966, you could buy either 1-cent and 5-cent wax packs or 10-cent cello packs.
The 1-cent wax packs obviously came with only one card except in 1951, when they actually came with two cards.
The 5-cent wax packs only contained 5 cards in their latter years, but there are lots of suggestions that at some point, they contained up to 6 cards. So far, I haven't found any definitive evidence of when the change occurred, but I see a lot of different sites claiming one way or another. I think they might be doing it from memory though.
The 10-cent cello packs had 12 cards in the early '60s, which I can verify from live pack breaks.
Does anyone have any more information on when nickel packs went from 6 cards to 5 cards? Wikipedia says 1960 was the last year of 6-card nickel packs.