Ch. 8 CHECKMULTISIG validation

[jl2012]

In a 5-of-7, the 5th signature can be for any of the 7 public keys. The signatures do not have to be put in any particular order.

Not really. The order of signatures MUST be same as the order of keys. This is consensus critical, and it makes sure that m-of-n multisig will perform at most n ECDSA operations.

So in a 5-of-7, the 5th signature MUST NOT be for the first 4 public keys

see: https://github.com/bitcoin/bitcoin/blob/master/src/script/interpreter.cpp#L1025