Ok long boring explanation woman has arrived. :) Early in pregnancy, both boys and girls LOOK like girls. They have a clitoris and ovaries (both genders) The Y chromosome in boys is dormant until about 10 weeks and at this point in time, the Y "wakes up" and starts making testosterone. This testosterone turns the clitoris into a penis and the ovaries move down and turn into testicles. This process takes several weeks to happen and so when you come in to a nub guess too early, it is impossible to tell if it's a girl or if the "stuff" is in the process of turning into penis/testicles. That is why we say the nub may still rise, because it's really a clitoris that may or may not be turning into a penis if that makes sense.
At 12+3, you can't really TELL if it's on the rise or not. Now, some little dudes already are sporting a ginormous ding dong even this early and then you can say, ok, yes, that's risen, it isn't going away and that is a boy. But most other babies are still looking very girly at this point because the penis is not finished doing what it's doing
That nub, to me, is super girly. It looks like a girl to me (I'm sorry since I know that's not what you want to hear) but the thing is, 12+3 is too early. I am not saying that is a girl, not at all, it's really still too early to guess. The nub can still rise and often does, even occasionally into the 13th week (If you want to look at a couple nubs that did look super girly in 13th week but were boys, coralsky and californiadreaming are good examples)
I have no clue how anyone could look at those same shots and say there is no nub. There is a nub, it's just that it's too early to go either way just yet.