You could easily do a worthwhile doctoral thesis on the matter of "DEMAND". Lots of factors--- some definite, many subtle, comprise that most pivotal quality of a collectible. "Demand" can also evaporate over the years, or come roaring back, though the latter happens rarely.
Say, I took the trouble of checking out your registered 52 Topps set you're working on. Wow, lots of great cards. Especially liked your Jackie Robinson. It matters not one bit it was one of the three double-printed last series cards. The demand for that Jack is off the charts. In my opinion, it's 25 times better-looking than the vaunted 1948-49 Leaf.
Anyway, hope you find what you're on the prowl for right now.
---Brian Powell