How precise are measurements on floor plans?

I’m doing a floor plan with my contractors on an existing house where we will keep all the exterior walls but the entire interior will be gutted and all walls will be moved.

From version 1 to 2 of the plans, I noticed one side of the house gained 5” when I added up the dimensions of the rooms. The contractor doesn’t seem concerned, and even tho I asked him to have the planner recheck he did not. Is this something to be concerned about, or is 5” difference on a house plan no big deal?

Also how closely can I expect the real build to match up to the plan? For example if the plan shows one room as 14’7” across, how many inches +/- would be reasonable to expect once it is built?