Actually, that is what I was told too, but I was also asking about magazine carriers in the same email and I didn't want to confuse anyone here regarding something they might not be interested in. I was surmising that the "A" portion mentioned integrated a mag pouch in to the same holster, which is not something I would want or recommend to others. Her exact response was:
"You need the # 4A (A for added accessories)"
Googling their web site, I also see the reference to a Remora Series 4A "RFT" Holster (Pocket/IWB). I'm not clear if the "A" in this case is not the Artemis option (a.k.a. ART option) which has more material trimmed off around the grip area, and not the "A" for added accessories) which Jaqui referenced, and which no extra mag pouch is visible on the site photos for this model.
From a cached page:
Remora Series 4A "RFT" Holster
Clear as mud.