Good call on the WB salvage for your bag!. I've saved several just for doing that but haven't had the need yet.
I'll have to remember how you show that bag clamped up, I was thinking I'd have to glue two seams.
The seams you cut are indeed awesome, neat trick with the track saw 👍
I always wondered about the extra inch for melamine, perhaps because it is so easy to ding an edge and this way you can get a true 4x8 and the lumber yard doesn't have a pile of rejects?