I e-mailed Professor #3 a very gentle reminder a few days ago, put in terms of "I wanted to make sure that you received all the online application invites and that there isn't anything else you need from me that would be helpful to you in the process...blah blah blah." Reminded very gently that the first deadline is 12/1.
I have not gotten a response. I am freaking out. Maybe a bit prematurely, but still. The problem is that application #1 is entirely in paper form, with all materials including transcripts, essays, recommendation letters going out in one single packet mailed by me. Most of the others are some combination of hardcopy material and online stuff. I'm not as worried about those, especially since those deadlines don't start until 12/15. Grad school #1 therefore does not even know that I'm applying at this point, whereas all other December schools have absolutely everything already except for 1 recommendation letter. I hear that admissions programs are somewhat lenient about letters being late if all other materials were there early.
So what do I do? I can't exactly stalk professor #3, and seeing as I already sent an email I don't know what else to do that doesn't cross a line. It's way too freakin late to try to get a letter from someone else.