It's not what OP is asking though.
He already did that, thus raises his concern whether his old keys are still in the migrated wallet.
That was already answered "yes".

Also, it's not from "legacy to HD", it's from "legacy to descriptor", even HD legacy wallets can be migrated to a descriptor wallet.
Old non-HD wallets can be converted to HD with sethdseed command even if the user do not want it to be migrated to a descriptor wallet.