Can't Locate Old Addresses In Wallet. Need To Sign Multi-Signature TX.

[heads]

I can't seem to locate 2 addresses in my Electrum wallet even though my Master Public Key says they are there and I can locate them on the Blockchain. It seems they have been used and are from awhile ago (2016). I've changed my search perimeter in Electrum from the hundreds to the thousands and I still can't find them. I've also used ismine("bitcoinaddressgoeshere") and it comes up 'false' for both.

They are '17FU5dWn2ZnUt7LHLs5d1tpmGJJQP4hJR4' & '1MTt3Y9RYsqYhcvnfA1xHgeZW2Ru7XP6fF'

I'm trying to expand the search history in my wallet but it only goes to 2016-7-21. I need to locate these addresses so I can find their Private Keys and sign some transactions made.