The R-Line does not have the reversing camera as standard, only the Elegance does. That’s the case since the Mk2.5 facelift.
Once you have a build date, you can’t amend the order anymore. Even prior to a fixed build date, if you amended the order, it would reset your place in the queue – delaying the build, so that wouldn’t have been advisable either.
I doubt the dealer said that all Tiguans come with reverse camera, since it’s patently not true (unless it’s a really crooked one) for this model of Tiguan. Only the Elegance has it as standard, as well as the hot one (“R”, not “R-Line”). The rest only get beepers.
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.