Redoing a roof on a 1940's house

I have already paid for a new roof from a local and respected roofing company. After I bought the roof, I lost a few shingles in a wind storm. I went up to put a tarp on the area till the new roof gets put on. I noticed that instead of wood panels under the shingles I have what lols like to be 2x4’s running parallel to the house. Is this normal? When talking to the contracted, he mentioned having to replace some wood due to rot where needed. I tried to attach photos below, it is where the shingles came
Off. This is at the edge of the roof and the gap which was covered by shingles I believe was for ventilation. My fear is that the contractor didn’t know/realize my roof is laid with 2x4’s instead of wood panels and now I have a construction job instead of only a new roof. Any idea on if this is normal for an older bungalow home in Michigan.

Looks to me you have tongue and groove (not 2x4s) decking. Nothing to be alarmed about, very common for a house of that age (before plywood was the norm). Actually this type of roof decking is superior to plywood/osb IMO. Not really sure what I am looking at in the picture but can tell its not for ventilation. The slot for ventilation should be at the peak of your roof and run parallel with the house. If you did choose a respected company they shouldn’t have any issue with making sure it is venting properly at the end of the job.

Theyd probably just shingle over it and replace any rot with plywood. Nothing to worry about, get these roofs a few times and we just nail laminates over.