measure twice cut once

It's not the loss of a layer per se... it's the difference between the nominal thickness (e.g., 1/2" performance category) and the actual thickness after sanding (e.g., 15/32"). To confound things there is actual 1/2" plywood available... There are also performance ratings for structural uses, e.g., that 15/32" sheet may perform as a 1/2" sheet in structural applications. I'm not sure that stores like Home Depot that list the actual dimensions rather than the nominal dimensions help the situation... locally if I go into a yard that primarily caters to the trades and ask for 1/2" CDX (I can get fir or pine) they know what I want. Ask the same question in Home Depot and you may be told they don't have 1/2" CDX (as I have been though I finally did locate it on my own).

This situation is not different from the nominal and actual sizes of dimension lumber... as we all know a S4S 2"x4" is never 2"x4" but rather the actual size is close to 1.5"x3.5" However, the actual size of a nominal

2"x4" is not a sure thing either as surfacing can occur before drying (noted as S-GRN on the grade stamp) or after drying depending on the source. In either surfacing case it's close enough for rough framing!

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has lots of information on plywood!