The saga of my slowly moving cabin renovation continues to the bathroom. Originally there was some softness near the toilet from water damage. I pulled back the vinyl tiles, then removes the water damaged plywood underneath. Below that plywood was tongue and groove flooring that was damaged near the toilet, but otherwise fine. I removed the damaged planks and found another layer of plywood (Looks like 3/8") sitting on the joists that wasn't damaged. Looked at the joists from the crawlspace and they don't appear to be damaged. My question is can I patch the area where i removed the planks with plywood and then go over the patch and T&G flooring with cement board before tiling? Alternatively should I just rip out the T&G and put a new layer of plywood sub floor down or take it down to the joists?