The G1 Thoroughbred Lying Foal only has a few look-alikes, the browns and the duns. The three older brown models are the most difficult as the wide range of variations found within each run could cause identification confusion.
The easiest to identify are the duns.
The model on the left is from the 2000 Fun Foals gift set. These are darker, with a dried-mustard yellow body and dark red-brown points and muzzle. The other model is from the 1997-99 Mare and Foal set. These are a much lighter dun with grey points and a stenciled blaze and hind socks.
The brown crowd can be a bit more difficult. Both of the bays at the top are old plastic. The first is #5700 from the 1975-76 Thoroughbred Foal set. These models are usually a sandy bay with little to no shading on their legs, usually the latter. The mane and tail should be black to nearly black. Some examples can be dark enough to be confused with the Stable Set foal, while some can appear light enough to be a #5702 chestnut with unusually dark points.
The #3085 Stable Set foal is usually a dark, milk chocolate bay, again with little to no leg shading and dark mane and tail. They are generally more brown or plum toned than the #5700.
At the bottom left is the #5702 chestnut foal. This model was only available in old plastic; the other chestnut is always new plastic. #5702 usually is much more orange in colour with a mane and tail slightly darker than the body or self-coloured. #5306 from the New Arrival play set is more peachy in tone, heavily shaded and sports two hind socks.
Many thanks to Deb Walsmith and Sharon Walbridge for providing [pictures]!