Today I started out by checking the squareness and moisture content of the roughly milled parts for the workbenches. None of them had moved that I could perceive. The moisture content had dropped about 1% since I brought the stock into the shop. At 9% I shouldn't have any issues with unexpected wood movement.
I re-jointed all the parts and then started planing all the stock down to the specified 1 5/8". As I was preparing to rip the parts to width I noticed