No, but are you sure they aren't suffering attrition? With their endless manpower, they might be losing 5% strength to attrition and simply reinforcing the stack back up to full strength every month, and you wouldn't even notice a loss of strength. Also, bear in mind that the level of fortification, tax value and land tech level affect the supply limit in a province, and if it's your home province you get a big bonus as well. So a 77,000 stack sitting in a wealthy, fortified province in Austrian territory could suffer no attrition while the same stack in the poor province next door would get hit badly.