Dustin, I think each year Topps did much less of their last series, after what transpired with their landmark 1952 set and its last series "disaster" for them, and later, for us. Just think, if somehow Topps had held on to all those unsold cases of 1952 high numbers, rather than dispatching Sy Berger to take them on a skow and dump them in the Atlantic. However, Sy obeyed orders.
Too bad.
Back to your question. I think for us who collected back then (for me, 1961 - 1973) it depended upon where you lived, and if any of your regular card outlets decided to order boxes of the last series. Also, if other kids got to them before me, and bought them all out. Finally, if I was able to be there at the market with my mother to select them, I had a chance. During 66-67, I simply ordered them through the mail from The Trading Card Company, in Farmington Hills, Michigan.
My personal favorite of the high numbers is also the 1961, the first year I began collecting baseball cards. For a number of reasons, I only got one pack of the 7th series. I loved how the cards looked that year, and Topps had so many interesting sub-sets. as well as multi-player cards. They should have done an "M & M BOYS" of Roger Maris and Mickey Mantle! Every kid worth being called a baseball card collector would have bought packs like crazy just to have gotten that card! It should have been made, but was not----dumb.
Finally, especially with respect to PSA / SGC high-grade survivors, their rarity depends upon how many of the few collectors that saved unopened boxes from that year opened them and had the best specimens graded. Moreso whether or not any finds of unsold stock occurred once the organized adult hobby began from 1969.
Once the landmark Mr. Mint find of 1952 Topps high numbers occurred in about 1986, everyone in the hobby, as well as many other non-hobby people due to the mainstream media attention from the find, were on the look-out for any cases or wax and cello boxes of old trading cards of ANY kind. Those few finds were in all likelihood the source of the future PSA 8s, 9s, and 10s.
I don't know what your objective is, but high numbers have always made for interesting discussion and great sea stories.
---Brian Powell