You might try looking through a cross-section of each style of glass as you are working. Even if it's hard to tell them apart looking through the 3mm depth of the flat glass, if you look at it on edge, it should be easier to identify.
I keep a Sharpie nearby to label all scraps as I go along with the cutting.
To prove whether this is what happened, you could cut a small piece of glass from your originally labeled sheets, set them up in the arrangement you were trying for originally, and fire them. Otherwise, we might never know for sure!
Mary Kay Nitchie
Bullseye Glass Co.
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