First, check your deposit agreement. It might have language in it that requires the depositor to check monthly statements and notify the bank of any errors within 30 days.
It doesn't necessarily stop the claim as some state's UCC laws state that a depositor has up to a year. But there are also other provisions in the UCC that adds neglect to be the liability of the customer.
Considering that he wasn't upset about it until he was upset about the girlfriend would make me say, "Nice try." I would also ask him why he didn't report it sooner. If he says that he didn't check his bank statements...well...that ends that as he didn't follow the deposit agreements.
I say that if they happened that long ago, you don't owe him a thing.
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My opinions are definately my own. I could be wrong. But I don't think so.