I just stumbled upon @version (to be used on TEI or teiCorpus) that holds "the version of the TEI scheme". The description for data.version reads: "The first number supplied identifies the major version number. A second and third number, for minor and sub-minor version numbers, may also be supplied"
Well, if I understand correctly, the current version is TEI P5 1.8.0 but I'm unsure what the major version number is - is it the 5 or the 1? (I may be not alone with this confusion since the example for tei:TEI gives @version="1.2.0" and for tei:teiCorpus @version="5.2")
Actually I do guess it's the 1 so my question is more a proposal to promote the version number more prominently and/or put into the value description for @version some information where to find the number, e.g. "if you downloaded a schema customization from tei-c.org it's called 'Edition' within the rng-schema" ;-)
All the best and a happy new year!