Okay, I posted the bottom part of this post on the overall FPP question thread so will repeat it here but also will add some SDFP specific things:
I tried with various accounts/people and my conclusion today at Epcot (this is my third day of playing with the Tiers) is:
SDFP Specific:
1. I tried as asked to book a Tier 1 SDFP at a kiosk, use it, then go back to the kiosk and see if I could get another one. I could not. It recognized I had already had a tier 1 and only allowed me to make 2 more Tier 2 choices, just like with a regular ticket. I tried to make a Tier 2 and change it, but of course could only get a Tier 2 alternative. I could not change SDFP's to another park (without going to that park) or book an additional (within the first 3) without going to a kiosk. I could still make changes on my app within tiers.
2. The issues I posted earlier about not being able to change SDFP's on my phone for people I didn't manage (who had their own Disney accounts) were my fault. Although I know at some time these people had their accounts set to allow me to see "All" their plans, both I tried had changed back to allow me to see only "Shared" plans. Neither person had any recollection of changing this and I had to give them step-by-step directions, but once they did I could now see theirs. So this hasn't changed but just throwing out there my problem with it in case anyone else runs into the same thing.
Some reflections on Tiers that don't have to do with SDFP:
1. If you book anything less than 3 FPP's (2 Tier 2 and 1 Tier 1), you will not be able to get a second Tier 1 at the same park. You will be able to get a Tier 1 at the other park (DHS or EP) if you cancel any remaining FPP's (or didn't book them in the first place). If, however, you try to only book/use the Tier 1 or you book all 3 but then cancel the other 1 or 2, it will simply show (either on your phone or at the kiosk) that you have already selected one from that category and only give you Tier 2's to choose from. Again though, tiers don't seem to carry over if you switch parks so if you book a Tier 1, use it, then cancel the others, you can immediately book a Tier 1 in another park.
2. HOWEVER - I did find out today that as long as you're past the window for your Tier 2's, and use your Tier 1, you can then book another Tier 1 in the same park. But...once you do that, you lose the Tier 2's. They still show but every time I tried to see if I could change them to a later time then I got an error message. So I booked Turtle Talk for 9:30, Pixar for 10:30 and Land for 2. Once I used Land (I didn't get to Epcot until almost 2) I could immediately book Illuminations or Mission Space (or other Tier 1's). But although my 9:30 Turtle Talk still showed, it wouldn't let me change it. So if you can arrange your schedule to get past the time windows, you could effectively only ride one Tier 1 and then get another one. But then you'd be stuck in the "one at a time" thing for the rest of the day.
So you don't actually have to USE all 3 but have to be past the window of all 3 or used them all.
Hope this helps and please let me know if anything isn't clear!
@hiroMYhero @ScrapYap