The better ones WILL!! But, as you say....if you start with the known phase as phase 1 then it's a simple matter of finding the other two phases sequence. The problem comes when all conductors are the same colour. Which is why many such installations are phase coloured throughout the entire installation.
Remember, on the MV side of things, it's difficult to keep the RST sequence, often to achieve that sequence, the incoming cable needs turning. So in reality, the actual sequence on the LV main panels can be anything but RST, but can sometimes still be distributed as RST but could well be TSR for argument's sake....
Look , all i'm trying to say is, that in quite a few situations Sequence is very important in particular scenarios!!!