so the limit automatically goes back to 140km/h in the absence of signs to the contrary.........
you seem to be just emphasising my point, it wont be obvious to them at all what the speed limit is. It may be to you as you seem to read the Polish highway code each evening and drive here regularly but it's not to a stranger. Why they can't have an explicit speed limit sign to remind you at least every few km's is beyond me, would probably help road safety too. Even the signs to signal a town or motorway are not actual speed limit signs, they're pictures - great, more guessing, what a help!