This comes up a bit...the main thing to think about is the sheer number of Peachies which would have been created. She is perhaps the most common G1 pony, she was released in multiple years, in multiple ways [store bought, mail order] and. in just about every country that got China/HK MLP, the Pretty Parlour turned up. In addition 30 years of play and store in different ways means a ponies pigments and plastic will have different experiences and perhaps different degradation.
For this reason you do get a lot of variety in symbol pigments, plastic shades and even size [due to plastic shrinkage] - that is probably all this is.
However, it is also a good excuse to start a Peachy army!