It is my general understanding that, with the exception of intra-European flights and, to a lesser extent, intra-US flights (which the airlines do not allow earlier standby, to preserve the "value" of fully flexible tickets - as in, if they allowed earlier standby to even cheap tickets, airlines think less people will buy the flexible tickets and go for the cheapest), most airlines adopt a slightly different set of rules depending on before/after you turn up at the airport.

By that, I mean that if your ticket is non-changeable, you would normally get the "no" answer from the reservations agent. But come the day of the flight, if you turn up at the airport early, they quite often overlook the ticket restrictions if the earlier flight has plenty of availability. Especially so if the later flights are booked more heavily. In a way, it also makes sense for them to "fill the plane as people come", so to speak, so that on the later flights they can accept more standby pax and improve the load factor.

But since you're talking about airline bending published rules, nothing is really concrete and depends on a host of factors, not the least the mood of the person you ask. So I guess the answer would be, "It is possible, even likely, but your mileage may vary".