Installing reverse board and batten plywood siding
To me, board and batt means the larger board goes on first and the smaller board (batt) goes on second and laps the edges of each board. Likewise, reverse board and batt means the small board (batt) goes on first and the larger board goes on second and covers the spaces between the batts. 

Over the years, we've learned that using plywood for the "board" and just installing batts at regular spacing on the plywood will give the same affect as "board and batt" siding...for less cost and fewer problems because the "boards" are wide and tend to split (check). 

I'm not sure I've ever seen (or understand) how reverse board and batt works with plywood. Seems like installing large boards on the plywood with small spaces between them would defeat the purpose (and cost effectiveness) of the plywood. 

In any event, both systems are installed on a moisture barrier, like building paper, etc.  This is essentially your moisture covering over the walls and the wood board and batt (or reverse board and batt) is just to keep the moisture barrier protected. Protected from wind blowing off the paper, UV protection, etc...  

So, just as @isherwood says, you don't need to "seal" the vertical joint. It will be covered by the batten, or in your case, covered by a board. 

By the way, we've learned to extend the moisture barrier about 1" past the bottom plate so water doesn't run out the bottom and blow back up under the bottom plate. If you live in a high wind area you'll want to put a felt pad between the plate and the top of the concrete stem wall to make a better seal against wind blown rain. 

Also, we've learned NOT to caulk the bottom of the board and batt to the horizontal Z metal. Rather, we want that moisture to run out. After all, we know the board and batt (or whatever is above the metal) will leak. That's why we install a moisture barrier under the siding. If you caulk...you'll get dryrot on the bottom of the siding that sits on the Z metal. (We use a peel and stick membrane to seal the metal Z flashing to the upper moisture barrier.)