i've never had problems with standing by for/at co-terminals.

example 1: i am at houston and want to fly to LaGuardia instead of Newark or vice versa. never a problem.

example 2: i drive to fort lauderdale instead of west palm for my return flight to newark. again, never a problem. the ticket agent doesn't even blink when looking at my ticket. i get a standby boarding pass to get through security. easy as pie.

i am not saying this is normal or correct according to the ticket rules, i am just giving my experiences.

and, i have had non-refundable/changeable tickets for each of these examples.

maybe CO Insider can share this thoughts on standing by at/for co-terminals.