I think it's T-72.

At least, that's when it appears to show as available on the seatmap in MMB. Up to that point it looks as if it's taken. But once it appears I can't actually select it because it disappears once you click on yourself to move there.

In those cases I ring the gold line and they sort it out for me.

Not sure if anything's changed with the new seat plans though. I just checked - on my flight Monday the bassinet seats appear available as normal (under t-72) but disappear when I click on my icon (as before). However, they don't reappear once I click off my icon which they certainly used to. So who knows what the scoop is.