Pyrex Passion author Michael Barber recently wrote on his blog about being asked if he had noticed variations in the decoration of the Friendship 473 round Cinderella casseroles. Like perhaps most of us, he had not. But a quick check of his collection verified it was true. The birds at the opposite ends of the decoration have either a single red "flourish' or a double orange one above each. Since the lids for the Friendship casseroles were changed from decorated clear glass to decorated opal during the pattern's production, it might be tempting to assume a change in the pattern on the dish coincided with that. I was able to find another instance of this curiosity, but am afraid it really provides no answers, just more questions.
The photo above is from the 1973 Pyrex Canada catalog, showing all decorated clear glass lids. You can see that each round casserole set contains a different variation of the 473. Curious is that a replacement parts listing in the same booklet lists both clear and decorated opal lids as being available for the round casseroles. Even more curious, it lists only opal lids for the oval casseroles.