were the plans originally meant to be printed at a3?
All our drawings are done at scales @ A1. Normally states this such as "1:20 @ A1" Or somewhere in the notes/drawing border it states that all scales are a1. There should also be a scale bar for each scale used on the drawing, so you can confirm everything.
Either way, they should also state "do not scale" on the drawings, since print outs are never accurate, the dimensions are what matter.