Well that explains some of the people in the corrals ahead of me. I was in the E corral last year for the marathon and quickly caught up to some runners from the D corral, who obviously could not have run the 1:50 half that got me an E placement.
In addition to the other comments regarding spot-checking, keep in mind the volunteers on race day aren't 100% effective in preventing people from corral jumping. I've seen volunteers stand firm in redirecting people to their assigned corrals (further back), and I've seen people 2-3 corrals ahead of the letter on their bibs. That's not isolated to runDisney races, but I do suspect the nature of runDisney events invites more behavior like that by appealing to people more as a
Disney experience rather than a race; made more problematic by the appeal to non-runners who aren't familiar with etiquette, are less prepared for the race element, or who may not even care about the race element.
The nature of their runs as an
experience beyond a race also encourages experienced runners to run their races
slower than the potential reflected in legitimate POTs. My wife and I run local races for time because they're relatively cheap with little entertainment; we run faster to get it over it with faster. Disney gives us more to see going through the parks, so we're less concerned with our time. Picture
stops are an explicit encouragement to forgo pace and time for the races, which by themselves will result in various corral/pace mixes once you get into the parks.
With runDisney runs, I think it's best to go in assuming that you're going to end up around some people who are slower than you and some people who are faster than you, for one reason or another. Keep an eye out for safety, but otherwise try not to worry about what other people are doing and enjoy your race for whatever it is to you.