It may be that the later versions of the 3120 (like in your 15400) tried to correct this somehow but it’s best to be careful. (Rolex is the only watch I have where no care is needed during the date change and you can even wind it backwards to the preceding date without any issue).
Audemars, and in particular the 3120 in-house movement, is sometimes criticized as being a bit finicky and unreliable. I have to disagree. It’s now been 10 years (bought it new in box) with my 15300 and it’s been absolutely bullet proof without and issues and is within COSC specs despite never being
I think it’s important to remember that it’s not an expensive watch at MSRP so, understandably, the finishing it nothing special. It is very utilitarian. That said, the tolerances internally and externally are perfect, and perhaps the best evidence of that is the /- 2 seconds per day accuracy.