The pic you show has a very large side-getter patch (good), with light-gray fringes that indicate some light use - roughly consistent with the seller’s description. As use continues, the side patch typically shrinks (well before the top patches), with the fringing sometimes becoming more dominant. I have some GE 7581A with chrome side patches and NO fringing, that are probaly truly NOS. Anyways, to see a very large side getter patch on a power tube (dark metallic or chrome, NOT chalky white/gray or brown) is usually a good sign. (note: if you see a side patch on a tube that shouldn’t have a side getter, like an EL34, that’s bad news lol)
The debate on "NOS" nomenclature is boring semantics. NO I wouldn’t call this tube strictly NOS, but these days very few tubes left are. If the seller’s description is accurate, and seller can be trusted, I’d be happy with ’em.