It was a very long and difficult journey, but I have finally done it: My solutions have all been accepted by Icho, and so I have officially 100% resolved all of United!
A year and a bit over a month since the 1 year anniversary of when I started taking on United. Just getting the official confirmation from Icho himself earlier today nearly got me teary-eyed. So, I have officially completed one of the hardest level packs out there, although not without a bit of help along the way in the form of subtle verbal hints on a few levels.
Interestingly enough, I'm currently taking on LWT for Old Formats, and this pack barely inches out in the lead for largest number of levels solved in a pack thus far. I have completed 240 levels in LWT, while United is at 238 levels, so just two levels ahead. There's still two more ranks of 40 levels each in LWT that I still need to solve, but I'm currently awaiting a pack update. Hence, proceeding with the rest of the pack is currently on hold until that happens. In the meantime, I will be solving/resolving contest levels and playing other packs, as well as test LOA, in the meantime. Whereas for what pack I'm going to tackle next, I have yet to decide. Most likely another pack for Old Formats.
I have updated the OP to reflect total completion of United.