Almost every signage problem we are asked to fix started with a sign made to a drawing rather than to a building. Buildings are not square, substrates are not what they look like, and the power is rarely where you assume.
A survey takes about an hour and settles all of it: real dimensions, what the wall is actually made of, whether there is a supply and where the isolator can go, how we get access on the day, and whether the sign needs consent.