When I went to the lumber yard for my project, I grabbed my sheets from the 3/4" MDF pile. I checked the first sheet, to make sure it was the right size and thickness, and then grabbed the next two sheets from the pile, as well. However, the other two sheets were not 3/4"; they were 5/8". I'm not sure how that occurred.
By some ridiculous stroke of fortune, only the joining pieces and interior stuff ended up being cut from the 3/4" sheet. All the parts with a visible edge - the side panels, the control panel top and box - ended up being cut from the 5/8". Sigh of relief!
Well, I guess the worst that might have happened is I would have had to buy two sizes of t-molding. But still, I'm happy to have escape that fate.