Does the API ever return an <issue_number> that is not a number? i.e. "A", "B", "II", "IV", "18a", etc. If so, can someone please post an example volume? I'm writing a parser and don't want to write logic to handle non-numeric characters if I don't have to. It would make sorting substantially more difficult. Examples that come to mind, but are not reflected in ComicVine are the "error" issues in the Sandman series. In every guide, they're listed as 8a and, I believe, 19a, but there is no mention on ComicVine that I saw.
I'm not sure, but I think the form validation on adding new issues requires the issue number to be an integer. CV doesn't handle variants as different items, so there's no Cover A, Cover B, 2nd print, etc. The comic guides track variants because there's different prices associated with them. At CV, they are just tracking the issue and not the costs, so they don't list each variants.