They used to spred out the potter putty over the initial laminate and put the blocks in leaving a small gap in between each block. Then they spred another layer of putty over the puzzle where by sealing in between each block... then laminate over that...the theory was that should one block get some rot it would not spred to the others. Also a whole sheet of ply would be harder to get to conform to the part shape then the blocks. It made for a heavier part but it worked...but in this day and age why not go composite I say
strick