I'll try to say this without spoiling anything:

We're in a mission where the mission instructs us to "set aside X tokens" of a particular type. Some things case those tokens to be discarded, but none of those events have triggered. All X of those tokens are assigned to the rebels. Later, a card allows the rebels to claim one of those tokens.

Do the Rebels get to claim another token (so that they will have X+1 tokens)? Or are they limited to the X that were set aside in the mission rules?

I know the RRG p8 indicates: " Tokens are not limited. If players run out of a token type, they should use a suitable replacement, such as a coin."

However, were weren't sure if this particular instance is special because the mission only told us to set aside a certain number of this particular token, or if it's just like any other type of token.

You're limited to the amount the mission set aside. Which is why it has rules for discarding, to limit the amount the rebels can get.

But what card? That's one that does make sense. Or did you mean a mission rule?

If you set aside X rebel/imperial/neutral mission tokens, only those exist for the purposes of mission rules using those tokens.

It would help if we knew which mission.

In fact, no mission uses more mission tokens than are available. All missions are written to need only the amount and types of mission tokens in the game. The component limitation rule thus becomes relevant only for strain, damage, and condition tokens.