Trying to recover a July 2012 Bitcoin wallet need advice

Need advice from Bitcoin community about a 2012 wallet recovery.

My client has a Bitcoin address from July 2012. We have a 12 word seed and the password, but nothing works. All 12 words exist in both the Blockchainwalletv3 list and the BIP39 list, and no word is missing.

But when we try to recover it on the Blockchain.info recovery page or other tools, it always says invalid seed phrase.

We also tried several recovery tools from GitHub including btcrecover:

https://github.com/gurnec/btcrecover https://github.com/3rdIteration/btcrecover

But still no success.

The confusing part is that some sources say 12 word seed was very rare in 2012, and some say it did not exist at that time and only wallet identifier, password and wallet json were used.

Because of this we are thinking maybe my client misunderstood something about the seed, but the 12 words look valid and match the word lists.

Right now we are only trying seed shuffle and some brute force tests, but honestly we almost lost hope.

If anyone from the community has any idea, suggestion, or experience with old 2012 Blockchain wallets, please share. Maybe there is something we are missing.

Thank you.