This is an excellent question but not one that I can answer officially, aside from to say that as far as I understand things there is only one official version of each version of EAD at any one time. And so far EAD has had, essentially, two major versions: 1998 and 2002. Those versions are rarely if ever updated, however, so I think you're safe to use http://www.loc.gov/ead/ead.xsd (or the RNG file) without worry.
But, as you may have already heard, the third version of EAD is expected to be released in 2014. I don't know if the official URI has been decided upon for the new schema, but you can check out its alpha version on GitHub at https://github.com/SAA-SDT/EAD-Revision/blob/master/ead_revised.rng
Basically, though, if you validate your METS records against the current EAD 2002 version of the schema, I'm pretty confident that this version will never change on you (although I don't know how long it will be supported, so I don't really mean "never," of course; I expect, though, that it won't be going away too quickly, since it will take some time before the next version of EAD overtakes the use of EAD 2002).
I hope that helps, but if not, someone else can hopefully address this question more thoroughly.
From: Encoded Archival Description List [mailto:[log in to unmask]] On Behalf Of Vicky Phillips
Sent: Wednesday, April 03, 2013 6:20 AM
To: [log in to unmask]
Subject: Version specific EAD schema
We are currently working on a project in which we will be using the EAD Schema within METS and I have a question regarding referencing specific version of the schema. We do not hold copies of schemas locally, usually when referencing the schema locations we place the URL to the specific version of the schema itself (e.g.
http://www.loc.gov/standards/premis/v2/premis-v2-2.xsd) rather than general URL which is not version specific but retrieves latest version (e.g.
http://www.loc.gov/standards/premis/v2/premis.xsd). In doing so we ensure that the METS doesn't become invalid if there is a change in version. Can you tell me if EAD releases version specific schema similar to PREMIS? I've had a look around but can't seem to find any. Any help would be greatly appreciated.