It seems you made a small mistake but otherwise it’s all good 🙂 Have a look at the USDA entry for cooked glutinous rice. It lists values for 100g. When you enter “0.87” in the “Value per …g” column you’ll get the values for 87g, and it says 18g carbs.
yet the rice I have is 100g to 42g carbs?
Nope, because as you wrote the label said 52g have 42g carbs.
BTW, food that was cooked is harder to compare because of the fact that water is relatively heavy 🙂 Practically all types of rice have similar raw values (some have more fiber though) of about 350kcal per 100g uncooked rice resulting mostly from 80g carbs (80g * 4kcal/g = 320 kcal, the rest comes from protein, fat + fiber). So, the label of your “Sho-Chiku-Bai” seems correct.
What differs is the cooked result: 100g rice may easily end up as 200 to more than 400g of cooked rice. Different kinds of rice will give different values, however, the differences due to cooking methods and personal preferences may even be larger. The USDA lists
cooked long-grain rice and cooked short-grain rice with the same calories: 130kcal/100g — which means 100g uncooked rice resulted in 270g of cooked rice. The value for glutinous rice is 97kcal which means the end result of 100g cooked rice was 381g. Compare this with what you got:
1 cup [208g] of dry rice makes about 400g of cooked rice
Roughly, that’d be 200g compared to 381g (unless you actually meant a cup of 100g).
In short, my advice: If possible relate to raw values.
I, too, prefer to buy food with nutrition labels. White rice is an exception, though. The nutrition values, as I said, are always the same within a range of +/- 1g. So, I buy sacks of 20kg from Asian specialty shops where I get AAA quality Jasmine rice (often even cheaper than from all-purpose super markets).