At the very least, you've successfully performed an experiment that even with the default of 14days mempoolexpiry setting,
some nodes will still keep a would've dropped transaction in their mempool that will eventually be relayed to miners in the right network conditions.
It could have been the Trezor server. I don't know what their default is, but I assume they keep broadcasting all transactions until they get confirmed (or replaced). I assume exchanges do the same, just like my Bitcoin Core keeps broadcasting transactions forever.