Raymond, that's a decent summary of the history of the finale of Amazing Races with certain exceptions l will address below, but first I want to address your inference that seasons 1, 4, 5, 6, 7 and 10 all had trailing teams and that's why it was a 2 team race to the Finish Line. World Race Productions clearly has a goal reinforced by constant bunching throughout each race to reach a 3 team competition in the finale. The only instances with only 2 teams and extraneous factors were not responsible is "None of the above":
AR1 - Joe/Bill were 24 hours behind and had no chance of catching up
AR4 - Dave/Jeff fly to Sydney instead of to Tokyo and take themselves about 24 hours out of contention
AR5 - the infamous disallowal of Colin/Christie and Brandon/Nicole on the United flight Denver to Dallas only due to the baggage check-in issue; also the fact that this is a genuine 3 team race with Nicole/Brandon maybe 10 minutes behind Colin/Christie at the finish line
AR6 - Adam/Rebecca lag slightly behind in Hawaii
AR7 - Ron/Kelly were even until they miss the exit ramp for San Juan International Airport
AR10 - Lyn/Karlan could not get a seat on sold-out Air France flight CDG to JFK and had to settle for an earlier leaving connection through Dublin to Newark
On the question of your season-by-season summary:
AR1 to 4 - OK
AR5 - Colin/Christie and Brandon/Nicole were denied the right to fly on the United flight Denver to Dallas due to baggage regulations and their checking of their stuff back in Calgary on American Airlines, on whom they were originally ticketed to fly. They were on the same flight from Calgary to Denver as Chip/Kim. It was the flight and not the limo driver problems that caused Colin/Christie being behind.
AR6 - you have cause and effect wrong. The cause of Jon/Kris being behind was their poor decision on which flight to take from Honolulu to Hawaii. The train was superfluous and merely reflected the difference in flights.
AR7 - Uchenna/Joyce and Rob/Amber were able to take the same flight from San Juan to Miami. Soon after arriving, they took different paths through Miami's Little Havana Cuban section. Uchenna/Joyce gained about a 45 minute lead there, most of which they used up in trying to beg for the remainder of their taxi fare from Miami to Ft. Lauderdale. From Little Havana to Ft. Lauderdale and from the bridge jump back almost to San Juan International Airport are the only 2 points where where Uchenna/Joyce were actually ahead in the finale of AR7
AR8 - there was no footrace that I remember. Nick Linz had to run for a very minor amount of yards to reach the Finish Line while Wally Branson had to finish the puzzle.
AR9 - OK
AR10 - the lead for Tyler/James over Rob/Kimberly developed as a results of the EZPass incident at a tollbooth in Queens on the way to Manhattan. They kept this lead for about 30 minutes in Manhattan and maybe 90 minutes driving to Garrison.
AR11 - it depends on what you mean by neck-and-neck. Eric/Danielle won by about 10 minutes over Dustin/Kandice, who were ahead of Charla/Mirna by about 15 minutes at the Finish Line. To me, that is not like AR2 which was real neck-and-neck.
AR12 - from the scale ROADBLOCK on, I saw no neck-and-neck here. I reemmber TK/Rachel winning by at least 10 minutes.
AR13 - this really was neck-and-neck in downtown Portland; you are correct that after Voodoo Doughnuts it widened to 5 to 11 minutes for Nick/Starr over Ken/Tina.