Purchase cost is the foundation
Cost basis records what you paid for each copy. It should remain attached to that copy even when market estimates change.
Estimated value needs relevant evidence
A sale is useful only when it matches the correct card, variation, and grade closely enough. Removing mismatches is more important than displaying a number at any cost.
Gain and loss are not realized profit
Estimated value minus cost basis produces unrealized gain or loss. Selling fees, shipping, taxes, and the final sale price can change the realized outcome.
Population adds scarcity context
Population counts can show how many examples exist at a grade, but they do not measure demand. Consider population alongside sale frequency and price behavior.