What a wine label pair carries
A wine sold in the United States carries its mandatory information on the labels of the bottle, and the TTB splits that information between the brand label, the label that carries the brand name and usually the front, and the other labels on the container. The brand name and the class and type go on the brand label, and the name and address, the net contents, the alcohol content, the sulfites and the government warning may sit on any label affixed to the container. This wine label maker turns that split into a front and a back you can design as one pair.
The front label is the label a buyer sees on the shelf. The back label carries the sentence that explains the wine and the small print that a shop, a distributor or a label reviewer reads. The wine label maker gives each side its own size, its own starter and its own type sizes, so the front can be the larger, taller label and the back can be a smaller companion that still holds the warning.
The rules quoted on this page are from 27 CFR part 4 and part 16, read on the eCFR, and from the TTB wine labeling pages. The tool shows what each check reads and the paragraph behind it. The TTB handles the COLA application; the wine label maker gives you the label files.