I just realized that when I sent BTC from Mycelium, it split the value from a source address into two target addresses, but the BCH of course stayed at the original address. I'm concerned that I can't verify that the private keys Mycelium tracks cover the spent address. If I export my Mycelium keys to a wallet that supports BCH, will it still be able to access the BCH that was at the spent address? The spent address (public key) is 1FfbdfD6bfwy1HXLTznGnUVsBTxZGMXDod and I can see Mycelium knows about the unspent output address that it still has, but I can't see what addresses it's private keys cover.
Mycelium uses a hierarchical deterministic (HD) wallet, which means all private and public keys follow from an initial master key value. Every time a spend transaction occurs from the wallet, you can see that another private key is generated from the master key and it keeps a count of how many private keys are used. Any application that can sweep such a wallet should be able to acquire all the private keys along with it. If not, other questions answer how to extract private keys from an HD wallet: Derive private keys from a HD key