I wouldn't consider stopping the concrete short of the wall and having stone to be drainage. Where is the water really going? Under the concrete and to the base of the wall with no place to exit? That is not ideal as it creates very wet areas under your structures where the water can do bad things (like freeze and heave your deck and/or wall if you might have any cold weather in Boston). I think you need to look at your decking plan and water runoff plan as a whole for the entire project area. I couldn't identify any in your wall constructions pics but did you install perforated drain pipe wrapped in fabric with stone above it all along the back of the wall areas to allow the water that will build up behind it to exit via gravity to a lower portion of the yard? For the decking, same concept. If not, you could, over time, be looking at wall that slopes towards your pool. You will want to ensure you have a path for all rain that falls on the decking to travel away from the pool area, either by drains or a natural flow off to the grass on the outside of the decking. Our pool is on a larger slope but considerable effort (mind and body) was put into how water would move around the whole area.
For the deck, I'd lean (pardon the bad pun) towards having the concrete go right up to the wall to provide some additional stability (in case it wants to lean - if there is no drain pipe behind it.) That's only a partial fix though. The real fix (again if no pipe behind) is to excavate and put pipe behind it (massive effort but better now before landscaping). The decking should be sloped away from both the pool and wall with either a channel drain system installed or multiple round drains. The round drains are a very difficult to get the concrete properly sloped for in all areas though. Ask me how I know.
Sorry for the candor - especially if you did install drain pipe behind the wall.