In Aug 2015, JP Janssen, the creator of OLGA, embedded a 20 kb, stamp-sized image in a Counterparty
broadcast, with the data split among 172 multisig outputs. Interestingly, these weren't "fake key" multisig outputs. They were consolidated and
spent in April 2017.
However not all multisig outputs in Counterparty or spendable; for what reason I don't really understand, but I would like to.
I don't remember technical spec of Counterparty. But since the TX show each UTXO is 1-of-3 P2MS, i expect 1 public key is real while 2 other are fake (used to store arbitrary data).
The problem with a cat and mouse game is that the mouse can iterate much faster than the cat.
Of course they could create a very specific filter for the OLGA protocol (which uses P2WSH) too, e.g. detecting the OP_RETURN metadata attached to them, but the problem with this approach is that "the mouse" can
always change the protocol, without any harm, because the existing NFTs are already in the blockchain, and it may even increase their value as "legacy" Stampchain NFTs. In the end you will be filtering a lot of legit transactions too, probably.
Interesting historic insight, by the way

I don't expect it'll filter monetary/financial TX, since OLGA require OP_RETURN or P2MS that contains Counterparty data and prefix "STAMP:".