The quilted cover
The pocket is the figure that has to hold everything else. A range gives a shallow and a deep end; a single number gives only the deep end. Eleven of the eleven cover listings state a pocket, seven as a range and four as a single number.
The eCFR text of 16 CFR Part 1632 defines a mattress pad, for that flammability standard, as a thin, flat mat or cushion, or ticking filled with resilient material, for use on top of a mattress. The site uses that definition to anchor the word and applies it to no particular listing.
Sizes are the other half of the check. Quilted covers here are filed in Twin, Twin XL and Queen. Nothing is filed in Full and King, so a mattress of those sizes has no pocket on this site to be checked against.