I should have been clearer; When looking at other formulas the term oxalic acid is used loosely;

From the British Beekeepers Association:

dihydrate must not be confused with dehydrate(anhydrous).

dihydrate is a compound with 2 molecules of H2o(water) in crytalisation in our case 71.4% concentration.

dehydrate is a compound with almost all H2O removed so is near to 100% in concentration.

My wood bleach is dihydrate , looked up it's MSDS.