Regular Run Stablemate Assortment
#5019 Standing Thoroughbred
This lady seems to get misidentified quite frequently. I've seen a couple of eBay auctions listing her as the 1990 Sears SR, have heard from someone who bought what she was told was the Sears SR, but received a #5019 instead.
The problem likely due to one of two reasons: A. if you are unfamiliar with the runs (and maybe hoping for a rarer model to sell), the RR and SR can look quite similar, especially if you are relying on reference photos which are unclear or maybe not as true-colour as one could hope, or B. you're using the 5th edition of the Breyer Animal Collector's Guide which has a few scrambled labels. Instead of the 1990 SR, a #5019 is shown, another #5019 is also shown with the #5650 Saddle Club II set label. The mare from the Saddle Club II set is listed as #5019 and the 1990 Sears SR doesn't seem to have made it into the line-up at all.
As mentioned in the Citation Look-Alike post, if it has dark legs, it's highly, highly unlikely to be the 1990 Sears SR (I hesitate to say 'never' because of the variation factor), and if it is new plastic, it's definitely not the SR. The SR is usually semi-gloss to satin and has a grey tint to the brown. This regular run is more of an orange-y tan.
#5019 was first released as a sandy bay with dark brown to charcoal forelegs. In the 1993 catalogue the model was shown as a chestnut with darker mane and tail, but body-coloured forelegs - this chestnut model continued to be used in the 1994 catalogue as well. It seems fairly safe to assume based on these dates that the chestnut version might rare to non-existent in old plastic.