I'm surprised that nobody commented on this topic.  Am I the only person who sees this topic as confusing?  Could it be that it is only a problem for those of us who consult the original work?

We still see concentrations recommended which vary all over the place.  Is this the reason?
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There can be confusion between the actual resulting acid concentration in water and the amount of dihydrate crystals required to achieve it.  This is likely due to the fact that the process has been developed by people with some chemical training and is practiced by people who may be less conversant with chemical matters, or who have been out of school a long time.

From Wikipedia

Oxalic acid is the chemical compound with the formula C2O2(OH)2 or HOOCCOOH. This colourless solid is a relatively strong carboxylic acid, being about 3,000 times stronger than acetic acid... Typically oxalic acid is obtained as the dihydrate. (emphasis added)

As can be seen in the figure below (not shown here), the dihydrate contains two molecules of water and weighs much more than the actual oxalic acid it contains.  The calculations below simply add up the weights of the atoms in each and show how much of the weight in 86 grams of the dihydrate crystals we buy is actually acid (50 g) and how much is water (36g).

Anhyrous Oxalic Acid: 1+1+16+16+16=50 
Oxalic Acid Dihydrate: 50+1+1+16+1+1+16=86 

From the above, we can see that to get the same 50 grams of oxalic acid, 86 grams of the dihydrate crystals must be used, compared to 50 g of the pure stuff -- thus the confusion.

Since the amount of acid used is very small compared to the water in the syrup, the 'water of hydration' may be ignored when calculating the water in the total solution, but since the water in the crystals is insignificant compared to the total water in the syrup, but since it is almost half the weight of the crystals, it must be considered in measuring the acid.
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