The specific situation I was thinking of was that a creature with no armor (Zombie Minion, maybe) takes 0 damage from the red dice in the attack, and would take 1 point of corrode, but because it has no armor it takes 1 point of damage instead.
It takes this damage during the same step of combat as it would take regular red die combat damage (step 4), because thats the step that resolves effects.
In this case, it doesn't seem like its the token causing the damage, but the rules of the Jelly's corrode ability itself. The ability rules cause the damage as an effect instead of placing the token, so it can't actually be the condition that's causing the damage (like it would be with rot), because the condition token is never applied, an effect is instead.
Jelly's reconstruct ability triggers when it "attacks and damages a coporial creature". Are you sure this doesn't count? Its the creature's attack effect that is causing the damage.