The toys are slightly upgraded versions of the Take-Along range.
Gordon, Emily, Murdoch, Spencer, Hank, Hiro (all versions), Freddie, Connor, Caitlin, Gator, D199 and Class 40 have a reduced number of wheels due to sizing constraints.
Belle has the most wheels of any engine (not counting their tender wheels), even though several engines have the same amount as or (in Connor's case) more than she does in the TV show. Her wheels are also solid blue instead of red with blue rims, even though some other engines before her had coloured rims.
The prototype Kelly was a repainted Max/Monty model with the breakdown crane added on.
The Storybook Car's prototype had yellow magnets.
Captain's model does not have a mast.
The Knapford station set has shed doors.
Salty's bufferbeam was red instead of yellow. This was corrected in the 2013 model.
Annie and Clarabel's wheels were white instead of black. This was corrected in their 2013 models.
Sidney's model is missing the warning panel underneath his face.
Emily and Molly's prototypes had six wheeled tenders.
Charlie's prototype had a black dome.
The Slate Loading Station is a re-coloured Load-n-Go set.
The front end of Victor's saddletank above his smokebox in flashback, sea-soaked, and partially-repainted form is black instead of yellow.
Luke and Norman have black buffers instead of silver ones.
D199's side detail is reversed compared to his other merchandise models.
Class 40's bogies do not rotate.
A prototype drawing shows that Sir Handel was going to be included in the Tidmouth Tunnel Starter Set.
In 2013, all the models were reissued with slight alterations to their models, most distinctively their faces and their wheels. These changes coincided with the moving of production from China to Thailand.
The prototype rusty Stephen had Dash's cab and bunker, a tall funnel, and a silver driving wheel.
Stephen's rusty model depicts him with a tender, despite him not having one prior to his restoration.
The Muddy Ferdinand set shows Ferdinand, The Lion of Sodor, a freight car, and then Ferdinand's tender.
Some of the 2014 models have circular magnets similar to the Wooden Railway line of toys.
So far, three characters exclusive to the Railway Series have been produced.
Timothy, 'Arry, Bert and the 2013 models of Diesel, Paxton, and Sidney all have siderods molded onto their sides.
Hank's model does not have a front coupler like other Take and Play engines and his television series appearance. Interestingly, Connor and Caitlin's models have front couplers, while their front couplers are concealed in the TV series. This is also the case with their Wooden Railway models.
On the 2014 collecters poster, Diesel 10's buffers are red.
The 2013 packaging features a picture of the engine in CGI, and engines who have not yet appeared in the CGI series are given a pseudo-CGI look on the packaging, with the exception of Harvey and Molly, whose pictures are of their model forms.
The buffers on some 2013 and 2014 models don't have any coloured prints on them, while others have prints that go beyond the raised area.
The packaging for Whiff's Banana Blooper, Stanley's Construction Clash, and Bash's Tree Tumble all say "As seen on DVD" with the Spills and Thrills DVD shown, but none of those engines appear in any episode on that DVD, much less perform anything resembling what happens in the stories.