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As DTWH? correctly notes, the AE was replaced by the VRSM. The AE required (IIRC) 10 "Certificates of Efficient Service" in any 12 year period - in other words, a reservist had to qualify for 10 annual bounties in 12 years. (IIRC, this was less onerous than a TD qualification, but was still a notable achievement.) AEs got a bar at 10 years' additional service, whereas the VRSM gets a bar at five years.
Other than the medal itself, the major thing that distinguished the AE and the TD (not sure about the RNR one) was that the AE / TD entitled the recipient to the postnominal AE / TD, and the VRSM does not; only the special Queen's Volunteer Reserve Service Medal (QVRSM) does.
So far, so boring. What was poorly done in the changeover was that if Officers had completed half of the qualifying period at the time of the changeover, then they could opt to have an AE. However, NCOs were denied this and had to have the "lesser" VRSM; a crass decision, really, and one that created lots of bad feeling for no reason at all.
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