You can set the gap limit with this command:
wallet.storage.put('gap_limit',[i]X[/i])
Or you could create a bunch of new addresses to see if its contained in there:
for i in range(0, X): print wallet.create_new_address(false)
false: for recieving addresses
true: for change adresses
I thought about doing this too. I'll try it if all else fails.
Are you sure this address was derived correctly? He may have used the derivation path for change adresses?
The standard derivation path for electrum is 0/0/ for recieving and 0/1/ for change addresses (i think).
This is a good question and I don't know the answer. I'll ask him and find out. Maybe he's doing it incorrectly.
Thanks for your answer.