if it's only $14, you are beating onward travel suppliers where you rent the ticket.
And for Jan's (and your) peace of mind: airlines know that not everyone will show up, especially if tickets were sold at such rates. That's why planes are sometimes overbooked. But it would be fair to say that the whole scene with unnecessary onward tickets does make it harder to predict how many people will actually come, which does indeed lead to more empty seats.
even at 77 I am not recommending donating money to airlines as if they were charities. Then get at least a fully refundable ticket and refund it after the event.
And donate the money saved to e.g. Trees for Travel.
If you get checked for proof of onward travel by your airline, normally they'll require it to be within 60 days. The actual rule is not as specific, but this appears to be the most common interpretation. The interpretation by immigrations we don't know, as they don't normally enforce.
But with a ticket 88 days out you have a good enough story to at least try. If you need another ticket, buy it then. Go prepared so you know what to buy. That's what I did when my 57 days return ticket wasn't good enough for Lufthansa.