A drum of Lil' Lisa Slurry can be seen in the water in "Bart Carny".
Kent Brockman refers to Mr. Burns' actions in Who Shot Mr. Burns? (Part One) and Bart Gets Hit by a Car.
You can clearly see that the check that Mr. Burns sent Lisa does indeed read $12,000,000.00 and TWELVE MILLION below that. If Mr. Burns was directly showing it to Lisa and the rest of Homer, how could he have thought it was only twelve-thousand dollars?
The twelve million dollar check Mr. Burns hands to Lisa at the end of the episode reads "4/27/97", while the episode aired on April 20th, maybe implying that the events depicted lasted only a week.