Originally Posted by
Daitheflu84
Have you used the Saudia site for selecting seats when it was a ticket purchased through Delta, though? Either way, thanks for the suggestion!
Looks like the seat selection interface isn't available on Saudia right now for the one Delta-purchased ticket I have open, but it does show me the seat assignments so I can confirm they were made correctly. So if you use the Garuda site to assign seats, you can then use the Saudia site to see if they "stuck".
Another clue is if you go back into the Garuda seat map and the seat you just picked is now marked as occupied.