In general, there is one fabric pattern/colour per letter in an outfit code.
Occasionally, a factory used a second fabric of a different colour/pattern for a letter, presumably because the original fabric was no longer available. Typically, one of the colours/patterns is harder to find than the other, as it was used for a shorter amount of time.
For example, Twin outfits T3C – There is a burnt orange version and a burgundy version. It is believed that the burgundy version is the rarer version.
However, the PMI factory swing dresses take this to an extreme! I have identified both an S and a T version of the PMI swing dress, along with THREE other patterns. That means, at the very least, one letter used three different patterns!
I wonder how many other patterns they may have used? How many other outfits did this happen with? I’m constantly being surprised by exceptions like this one.