I began thinking about this again for two reasons. One, Adrian Peterson just came within 9 yards of Eric Dickerson's season rushing record. With 348 rushes for Peterson and 379 for Dickerson, that comes out to a standard deviation for the combined rounding errors of 7.8 yards, and about a 12% chance that the 9 yard difference is entirely due to rounding errors.
The other reason is that Brian Burke pointed out in the comments of the original article that the rounding errors of plays in the NFL are not independent. The total yardage gain for each drive has to round off to the correct figure. From Brian's comment:
"One other way to state this is that if a team has 2 plays in a row, and one goes for 4.5 yards but is scored as 4, and the next goes for 5.5 yds, it can't be scored as 5. It must be scored as a 6 yd gain because the ball is very clearly 10 yds further down field, not 9."
I wanted to try to account for this constraint and see how much difference it would make.
Note: the following is mostly dry and math-related, so if you want to skip it, I estimate the chance of rounding errors covering the 9 yard difference between Dickerson and Peterson at about 14%.