Example of having to deal with something on the fly.
We had 600 sq ft added on about 7 years ago. The building inspector was called in for a framing inspection and failed it. The framer had used 2x4 on the base of the exterior wall frames, but the plans (in a foot note) had called for 3x4 base. No reason for the 3x4, but the engineers typically designed for 2 stories and ours was a 1 story. Possible fixes, tear it all down and start over. Possibly add 2x4 blocks between the studs (needs to be engineered and approved). What I did, called the engineeers who did our plans, they wrote a letter that stated 3x4 were over engineerred and they ammended the plans stating 2x4 were acceptable. I took the note myself to plan check, had it approved and I myself called for a new inspection. Inspector who showed up the next and signed off on the framing. Lost 2 days of construction. A general contractor would not move that quickly, they have other jobs going on at the same time.