Speaking as someone who does a lot of odd little contracts and expenses, I think a fair proportion of people probably inadvertently get their taxes wrong in small ways. I'm positive that if someone micro-examined my returns they'd find something wrong somewhere. Though I'd give fifty-fifty as to whether or not it was in my favour. That day I was paid by that US company - what was the exchange rate that day, did the transfer count to the rate when it was sent, or when I received it given I have one date on the paid invoice return, one on the bank statement... Who knows? If there's some minor ****-up in their tax returns, I don't see that as a moral indictment.
Oh I don't see it as a moral indictment either, just amusing.
I would say though missing two sources of income isn't generally taken as a minor oversight, it does show a reasonable degree of carelessness. Perhaps if he wasn't late he could have been more diligent
