I'm using btcdeb to understand script. I pick a old random P2PKH transaction form mainnet, and paste unlocking script e locking script inside. I know that this script is ok, because I can check on blockchain.

Than I Want to try with btcdeb and it works only if add flag

--modify-flags=-NULLFAIL

I expect the True at the end, instead I get 0x. Now, I did some research on NULLFAIL, but I don't understand the Problem. Before BIP 0146 the script could return false?