Could your TA call PCL and have them get the room you want, if you see it available? I know, they don’t want to call PCL either.
They should have a dedicated Agency line for TA’s to work with them, but mine said they do not have one for them.
Or, as suggested, book what you want for 3 and have the TA pick it up and straighten it out. If they can’t, cancel the 3rd person later. Sad, this is still an issue.
It could be a marketing strategy, as I’ve seen this happen, far out. Then, months later, if the cruise is not full, they open a few more (for 2) in that category for sale, that were once only open for 3. Maximizing revenue? JMO
We really don’t know, it could also be a programming error too. Not much feedback on this subject.