This post contains minor spoilers for The Great Race.
This is something that purely came to me whilst showering, and it's something that has been on my mind as people on Sodor Island Forums have noticed similarities between The Great Race and Thomas and the Great Railway Show. Then, I thought about every special to date (even the bad ones) in reverse chronological order - yes, even Magic Railroad - and believed that from the start, every Thomas special has had some level of Railway Series influence.
(Note: I'm discounting The Adventure Begins because it's a remake of RWS books rather than making subtle/blatant references about them. There might be some that I'm missing; I'd love to hear what you can come up with!)
The Great Race (2016)
Book #23: Enterprising Engines
Both involve Flying Scotsman in some capacity, and they feature him having a brotherly relationship with Gordon (although the special gives Scotsman more character than the book did).
Book #35: Thomas and the Great Railway Show
Both involve a Railway Show on the mainland; in the book, it was about engines on display, and in the special, it's about engines competing to see who's the best.
Sodor's Legend of the Lost Treasure (2015)
Book #22: Small Railway Engines Engines
Both feature the Arlesdale engines (at least, the original three) and rather than being shown how useful they are, they sing about their usefulness.
Book #34: Jock the New Engine
Again, both utilize the Arlesdale trio, but they also feature an engine screwing up (Frank and Thomas) and both engines work to redeem themselves.
Tale of the Brave (2014)
Book #21: Main Line Engines
Both feature Bill and Ben playing a major supporting role. They also feature one of the original seven (Edward and Percy) proving themselves when the big engines put them down harshly.
Book #33: Thomas and the Twins
Like the book, Thomas goes to Edward's branchline when a bridge on his undergoes repair and works with Bill and Ben.
King of the Railway (2013)
Book #20: Very Old Engines
Both utilize an engine built earlier than 1900 (Skarloey and Rheneas, Stephen). We even get flashbacks for both.
Book #32: Toby, Trucks and Trouble
An elderly engine (Stephen and Toby) is the primary focus. Both also end up in scrapes but get out of them (Toby derails at a level crossing, Stephen gets trapped in a mine).
Blue Mountain Mystery (2012)
Book #19: Mountain Engines
Both feature narrow gauge engines as a major focus (Skarloey and Culdee Fell Railways).
Book #31: Gordon the High Speed Engine
Both feature two diesels of the same class as supporting characters (Diesel and Paxton, Pip and Emma).
Day of the Diesels (2011)
Book #18: Stepney the "Bluebell" Engine
Both have a diesel as a threat to the steam engines in some capacity (Class 40 and Diesel 10).
Book #30: More About Thomas the Tank Engine
Both feature Thomas and Percy as leading characters, as well as a strain on their friendship.
Misty Island Rescue (2010)
Book #17: Gallant Old Engine
Both involve an engine getting stuck and they have to get out of that situation.
Book #29: Great Little Engines
Both involve an engine leaving Sodor, but they return by the end.
Hero of the Rails (2009)
Book #16: Branch Line Engines
Are there any similarities? All I can think of is that both feature a snobby character (Daisy and Spencer) as a major character.
Book #28: James and the Diesel Engines
Both feature an engine opposed to another engine (James to diesels, Spencer to Hiro), but by the end, the engine opposed to that other has their viewpoint changed.
The Great Discovery (2008)
Book #15: The Twin Engines
Both have an engine under threat - Douglas for fear of being scrapped, and Thomas for fear of being replaced by Stanley.
Book #27: Really Useful Engines
Both have tank engines as a leading focus (Thomas is joined by Percy and Duck in the book, and by Stanley in the special).
Calling All Engines (2005)
Book #14: The Little Old Engine
Both feature Rusty and involve steam engines being opposed to diesels.
Book #26: Tramway Engines
Both feature Mavis as a major character, and they involve a bit of steam/diesel rivalry (in the book, it's just Toby and Mavis, and in the special, it's more extreme).
Thomas and the Magic Railroad (2000)
Book #13: Duck and the Diesel Engine
Both have a diesel as the leading antagonist (Diesel and Diesel 10).
Book #25: Duke the Lost Engine
Both have a lost engine as a major plot point (Duke and Lady); the only difference is that Duke has some defined character and Lady kind of... doesn't.
General
Notice the pattern in the books referenced. Every special from The Great Discovery onwards references both a Wilbert book and a Christopher book, possibly until we get to the 2019 special, which would reference Tramway Engines (again) and Wilbert the Forest Engine. At this rate, the 2020 special will reference Thomas and the Fat Controller's Engines, and I presume both are anniversary-related.
By coincidence, every Thomas special (again, starting with The Great Discovery) is released 25 years after the Christopher book being referenced is published, most likely until 2021 with New Little Engine and (most likely again) James and the Diesel Engines. Also, if you subtract the smaller book number from the larger book number (38 minus 26, for instance), the difference is always twelve.
If we are to believe that the 2017 special will be referencing both Oliver the Western Engine and Thomas Comes Home (especially considering Oliver's cameos in The Great Race), then there's a chance that some of the following will happen: Duck and Oliver get major focus, Donald and Douglas and/or Daisy will have a small role (if you consider their upcoming roles in season 20), the special is branchline-centric and there's trouble on said line, there's a road rival on the loose, an animal making an appearance, weather trouble (rain or snow), and/or Thomas leaving Sodor for a while.
I don't know if I'm crazy or not, but I think I might've made a remarkable discovery in the Thomas fandom. What do you think?