Hyphens, En Dashes, Em Dashes

Q. According to the CMOS hyphenation guide, number + noun modifiers call for a hyphen, but what about noun + number modifiers? I’m interested in cases such as “stage-2 cancer” versus “stage 2 cancer” and “stage-C3 HIV” versus “stage C3 HIV.” My suspicion is that the answer is in fact to forgo the hyphen.

A. You’re right—no hyphen. You can find this advice in the “noun + numeral or enumerator” section of the hyphenation guide, which says, “Both noun and adjective forms always open” and gives the following examples:

a type A executive
type 2 diabetes
size 12 slacks
a page 1 headline