OK, Nathan Bedford Forrest's Cavalry Battalion was organized in October 1861 as a Tennessee unit with four Alabama companies. Good point. But, when it increased to a regiment, wasn't it designated the 3rd Cavalry Regiment, and not the 4th?

I did not read into the post that Sims enrolled in Russell's Cavalry. The post says Sims' "unit specified as only '4th'" and asked which unit he may have joined. If it specified Russell's, I didn't interpret that, even though they were neighbors, etc., etc.

In any case, there does exist a record for an "A. Sims" in Forrest's Scouts. This could be a match; since A. Sims was in Harvey's Co., and the widow kept saying he was in Co. "H" [Harvey? "H"?]. There is no surviving record for Alexander Sims in any other 4th, and I know it could have been lost. But, seems to me the possibilities narrow down to Jeffrey Forrest's 4th, Russell's 4th, Roddey's 4th, or maybe even Love's 4th Bn., if not Forrest's Scouts (I am unfamiliar with this last unit; just looking at the name on the roll).