As far as AVRT and "sobriety" goes, there is no such thing, certainly not as a psychological construct or a state of mind. You are either abstinent or you are not. The "RR: TNC" book still uses the term "sobriety" in a couple of places, since it is slightly dated, but from the context, it is clear that it implies not being drunk. AVRT is about abstinence, so within the AVRT paradigm:
Addiction Recovery = secure, permanent abstinence; nothing else.
It goes without saying that based on the Big Plan and the definition of the Addictive Voice, there is no such thing as one-day-at-a-time tentative sobriety. In the later book, "The Art of AVRT," this distinction is made even more explicit, going so far as to equate both sobriety and moderation with "Beast heaven," both rich opportunities to get completely tanked in the future.
That said, AVRT does not contradict legitimate medical uses for drugs. If you had surgery and needed morphine, for example, that wouldn't be a problem. If you kept taking morphine or some other opiate after surgery in order to get a buzz on, to feel that deep pleasure, however, you would be feeding your Beast big time.
Personally speaking, I tend not to use the term "sobriety," since it sounds ridiculous to me, just like "relapse" does. In common English usage, outside of the "recovery" ecosystem, nobody speaks of sobriety. When is the last time you heard someone who didn't have exposure to recovery groups or addiction treatment use the word "sobriety" in a sentence?