The biggest problem with some vitamins is that the tablet formulations that distributors make, are too hard and do not dissolve well. In the case of these sublingual versions of B12...they dissolve quickly for the most part, so the release of the B12 into the GI tract is enhanced. The Puritan's methylB12 for example are very soft and only need one or two chew motions to pulverize and are easy therefore to swallow. The photo on the
new Kirkland bottle which we have not opened yet, is very similar to the Puritan's tablet appearance.

I've called manufacturers in the past regarding some questions, and they have loose leaf binders with the specs from the source of the raw material, to consult. I used to call Perrigo (a large generic OTC company) and they would read me the print out, when I used to ask questions on gluten content. I'd also ask regarding magnesium mixtures, and always found no breakdown in % when oxide/aspartate/citrate etc mixes appeared on labels.
That is why I don't recommend mag products with mixtures of oxide and other chelates because whoever supplies these to the distributors, don't detail the ratios!

Calcium products are the most affected by hard pressed tablets. Used to be a test the consumer should perform of trying to dissolve a specific product in water. Nowadays there are the instant dissolve types, like Maalox etc...and those are the ones I use.

USP refers to the raw material being non-contaminated and pure to the USP standards for medicinal use.
Some very well known supplement makers, do provide for house labels. I know when I called the Schiff company they explained this to me. They had a specific SAMe product they only contracted to SAM's club, for example.(it did not appear on their website and I asked why). So it is very possible that Kirkland's is made by another company this same way.

Delmonte foods used to supply many food house labels for canned vegetable products.