I think the question is that if, for example, you are going from a 40 zone to a 60 zone and the car recognizes the sign saying 60, you should be able to move from 40 to 60 merely my holding (and, implicitly, then releasing) the "+" button. It should know to go from 40 to specifically 60.
To answer the question, no, I haven't been able to get it to work; but then, conversely, I've struggled to find when I would ever have any use for it.
I wonder if the requirement is for the sign specifically to have been caught by the road sign recognition system rather than just assumed by the sat-nav? I just don't know. Like I say, it doesn't bother me at all, but it's a fun side point!