Unfortunately, compliance with the plywood standards is only voluntary for
the manufacturer. For instance not to many years ago an "A" grade face
meant NO veneer repairs. Now some companies allow as many as 5 repairs and
still call it "A". There are a few manufacturers that use the old
standards. The finest Marine ply I have seen is Bruynzeel and SNBCC. Both
are extremely expensive but worth it for critical applications. You
usually end up having to buy it from someone like Harbor Sales and having
it shipped to you. The so-called "Marine Grade" stuff I have seen in
places like Home Depot and other do-it-yourself stores is a poor imitation
indeed. Full of voids and defects, often with thin face veneers. The
really good stuff can run upwards of $125.00 a sheet for 5/8" sheets!