I have a two-part question on installing a closet flange. My house is a mid-60’s split-level and I replaced all the copper DWV with PVC. The main drain is 3” and I used a 4” to 3” closet ell. I had to remove the old flooring down to the joists, replace with new plywood, and cut holes for the ell to fit through. The ells are not yet permanently installed. The closet flanges that I bought fit over the OUTSIDE of the ell, and with the flooring in place I see no way to adequately glue the flange. So first, I have seen flanges the glue into the INSIDE, and have also seen the ones with rubber gaskets that have threaded adjustment that are then pushed in. Are these acceptable, any preference, or am I missing something with the outside type flange? Second, I assume the flange ring should rest directly on the sub-floor, and then any tile, etc, would be fit around the flange. Correct, no? Thanks…

I don't favor inside closet flanges for the simple reason that any reduction in size chokes down the discharge path. We always leave at least a 3/8" gap aroundthe closet stub up to accommodate outside flange. however they do make inside 3" flanges so if you don't wish to open up the hole it will be acceptable.

"I assume the flange ring should rest directly on the sub-floor, and then any tile, etc, would be fit around the flange. Correct?"

Not quite. A closet flange mounts flush with the finished floor. Not that it really makes much difference. The toilet bowl has a 3 1/2" horn that will extend down into the stub up taking up any difference a recessed flange presents. Hope this answerers your questions.
Tom