In classic tempering, why does reheating chocolate after cooling not simply undo the whole crystallization step?

Answer: It leaves Form V seeds

It leaves Form V seeds ✓ — Correct. Reheating just below the melting point of the desired Form V can melt less stable Forms I-IV while leaving useful Form V seeds. Those seeds then bias later solidification. The payoff is that tempering is selective editing of crystals, not simply warming and cooling.

It preserves every crystal — This sounds close because tempering does preserve something, but preserving every crystal would keep the messy mixture. The cited step removes lower-melting forms and keeps the useful Form V seeds. The surprise is that a small surviving subset can steer the whole set.

It warms too little to matter — This is a plausible guess because the reheating is gentle. But gentle does not mean irrelevant: it is tuned to melt lower-melting crystal forms while keeping useful Form V seeds. The payoff is that a few degrees can separate a reset from a selective edit.