I have been experimenting with the schnorr combined signatures and I cant figure out how to directly determine the number of signers.

From what I am seeing, the combined pubkey will say any combined pubkey with any subset of signers is valid.

I dont see a clean way to get a specific threshold validation. Is the process to iterate through all the pubkeys from each signer to see which ones validate against the combined signature? Otherwise it seems that some sort of combinatorial explosion of combined pubkey needs to be made to find the exact set of signers.

but I only need the number of signers, not the exact ones, so I am hoping there is a simple way

James