Demand drivers
On-field or in-show performance, awards, nostalgia cycles, a player’s legacy, and broader hobby attention all push demand. A rookie’s breakout season or a franchise moment can move a card overnight.
Supply and scarcity
Population reports (how many of a card exist at each grade) set the scarcity floor. A thin high-grade population supports a premium; a flood of new copies or reprints can soften prices.
Why stale values hurt
Because prices move fast, a value — or an insurance schedule — from last season can be badly off. Slabline re-pulls comparable sales continuously so your collection total reflects today, not a snapshot.