Reposting the question from BitcoinSE, since didn't get a response there:

I understand not all private keys are usable as they fall outside of Secp256k1, but do they really matter when the master node or path being derived in BIP44 generates a private key which isn't usable as those nodes (keys at that node) are not supposed to hold funds?

Or is it just the actual address (external/internal chain of addresses under an account) that matters as those are the ones supposed to hold funds?

Or hitting a private key outside of Secp256k1 somehow translate into child keys being outside of Secp256k1 as well?