It's not normal practice to reuse your Bitcoin wallet's seed phrase to create altcoin wallets, if that's what you meant.
Now, I'll preface this reply by restating that I don't know much about altcoins because >99% are outright scams as far as I am concerned, but I still think it is very common that people reuse the same seed phrase across multiple coins.If you use a multi-coin mobile wallet as many people do, such as Coinomi, then you get one seed phrase across all your coins. If you use a hardware wallet, then you get one seed phrase across all your coins. I think it would only be if someone downloaded and used separate wallets for every coin (which I suspect very few people do) that someone would have different seed phrases for each coin.
That's enlightening! Then, I guess recovering the two missing words should work absolutely fine as long as the original owner did use the wallet for Bitcoin at least once. After recovering them, the seed could then just be imported into a trusted (!!) multi-coin wallet to get access to other crypto. Sounds like a game plan.