not always..
why would they issue you a sticker for the first (usually) 2 weeks, if they are going to extend it another 2 weeks just like that?
the whole reason you get a sticker is that they have reason to suspect your car is unroadworthy, so thry give you 2 weeks to either a) prove that it isnt, or b) get it fixed/off the road, they wont just extend it because you cant get there within 2 weeks.
if it happens that you miss the date, or you don't get an extension, then you need to ring up and get a permit ($15 for a 48 hour permit) to take the car to either a place of repair/work, or the pits themselves.
ps. do you have an external gate or anything? what about rim/tyre widths, are they the same?