Thanks for the feedback. I had originally looked at 1793, since it has the same date/day-of-week structure as 1811, but moving forward to 1812 it at first appeared to cleave closer to the story with the dates spelled out for Lydia's elopement and the its aftermath. The online calendar I linked to also came down fairly hard on the later revision side of things.
However, going back to 1793 and following it through to 1794, there are two important distinctions that make it the more likely date range. One is Easter, which in 1794 landed much later on April 29. This midpoint of Elizabeth's stay at Hunsford leads to a later departure, Saturday May 10. "A few days later" she then returns home Tuesday March 13, which works much better for the "second week in May" described in the novel.
Also, 1812 is a leap year. While the dates given by Austen aren't necessarily impacted and still line up OKish with those given in the novel, the days of the week change, creating some strategic differences that look to better fit the story (as makes since for the original writing versus quick later revision theory).
A prime example is the abbreviated vacation for Elizabeth and the Gardiners. Based on the passage of time listed as happening before and after certain key events, they should leave Longbourne around Tuesday July 14 if it's 1812, which gives them only four days of sight-seeing and one Sunday rest before they head for Pemberley. But in 1794, July 12 works out to the day of departure, which is a Saturday. Even with next day's Sunday rest, they get eight days to travel around (with at least one more Sunday off) before heading to Pemberley, which makes far more sense.
The only thing that doesn't really fit is Mr. Gardiner's express, dated "Monday August 2." The date and day of the week don't match up in either year. It looks a little better in 1812, simply because Mr. Darcy arrives at the Gardiner home on Saturday August 1, we might presume Mr. Gardiner began the letter on Sunday August 2, and then finished and sent it Monday August 3 (in such a hurry to post he forgot to change the date). We know from Mrs. Gardiner's later later the express was sent on a Monday, when everything was settled between Darcy and Mr. Gardiner.
In 1794, August 2 is the Saturday Darcy went to the Gardiner home, there was further negotiation on Sunday August 3, and the express was sent on Monday August 4. It's an odder epistolary mistake, since it presumes Mr. Gardiner began the letter on the very day of Mr. Darcy's arrival and then had two days before sending it (surely he could have revised the day?) But we can still chalk it up to the uncertainty and stress of the situation (and a rare flub on Jane Austen's part when concocting her timeline).
So I'm back to believing that 1792-1793 is the more correct period for P&P to reside (regardless of publication date).