If its just the area right around the old screws, you could go back a few inches and find solid particleboard.

If it wasn't sitting under water for a day or two, you should be fine just cutting the drywall off a few inches above its peak. doors etc should be able to be cleaned if they were not under for longer than a day or two.

(It is a 3 story building and this garden unit was legalized with the rehab permit & plans under which things are being done)Existing drywall appears to be half inch (so we are off by 1/8th of an inch) and it was never touched so I thought it can be left alone but now they want to cut it and check the thickness.Since they demanded that I tear down the entire ceiling to put 5/8" drywall per code, I suggested if I can keep the Half inch drywall and just add another layer of 5/8" inch which would make it much thicker then what they demanded.

However, this is just one code regulation to look at.An insurance carrier or lender may require the bottom plate to be bolted every 12 inches, usually 6 inches deep.

It looks like this wide crack (from the picture looks like is a good inch on one side then less on the other plus a vertical crack that seems to follow a brick wall against concrete slab foundation.  

The US standard of sellers having to pay for the buyers agent is a global anomaly (just like inches, pounds and cups) and makes little sense.

You should be able to buy 18 inch by 24 inch blank signs and the wire stakes to put them on.I Googled "yellow roadside signs" and the first link that came up is an ad announcing 100 signs for $89.Also, pulled up this link:https://www.biggerpockets.com/forums/87/topics/44116-where-is-the-best-place-to-get-blank-yellow-bandit-signs-

I have found that once they get an inch they will take a mile.

They are a combination of roof pitch, dormer count and sizes , covered porch square footage, attached garage, 16 inch eaves, 2x6 construction, driveway with sidewalk leading to front door and more.

Some shark bites and half inch  or 3/4 inch copper pipes.