I don't blame you for doing your homework. I did the same and just did the fluids last fall. I assume you have a TR580 CVT; you can check this by popping the hood and looking on the driver side above the flywheel on the bell housing (the trans...) should be a sticker identifying the trans.
! Ours is a 2.5i, so it should be a TR580 ... unless we got a free 'upgrade' to the TR690!
If you have the 580, should not have changed much. The CVT fill is an 8mm Allen key on the driver's side near the back end. The differential drain is obvious. Is there not another plug about 5 inches away labelled overflow? It's an 8mm Allen key as well. The diff fill on mine is on the passenger side, near the half-shaft at a 10 o'clock position using the half-axle as a clock face. It's also an 8mm Allen key.
Got it -- so the front differential fill plug is
on the (US) passenger transaxle area, at about the 10 o'clock position; I think that part of my problem has been with all of the black plastic under cladding, it's really tough to see much of anything ... I'll have to check again more carefully for the overfill plug. (I guess your Outback is relatively plastic free underneath -- or did you have to remove this for your change?)
The tricky part is that there is some plug on the driver's side near that half-shaft but it apparently goes into the CVT fluid pump.......... So, a precaution I take is to smell the plug, pretty obvious if it is diff fluid. I was even paranoid enough that I shoved my pen light in the fill and confirmed light through the drain!
Good idea regarding the 'smell test'; I plan on staying away from the driver's side transaxle, and since my understanding is that only the front differential has a dedicated overfill plug (unlike the CVT, which doesn't), I think that I'll be able to find the overfill with more inspection.
I'm guessing that you went with 75W-90 GL5 fluids in the front? I personally find the 2017 owner's manual confusing in this regard, and would think that (at least for a CVT-model), the front diff would be 'happier' with nominal GL5 fluid.