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I agree. Molding plastic isn't quite as exact as people think. You aren't going to get the exact same disc repeated. There are variables (plastic blend, drying, shrinkage, etc) that can affect the stability of a disc.
As a generalization, I feel like Katanas have gotten beefier lately. Years ago I'd throw Katanas and they'd all be flippy, sometimes overly so. Now, when I throw Katanas it seems like 50% of them are really overstable and glideless.
IMO, the Katana is perhaps the most finicky driver mold on the market. Any time you take a very wide rimmed, somewhat understable driver, the opportunities for variance arise. Of the last 3 Katanas I've thrown (2 champion, 1 star), the 2 champions were very overstable and glideless. The star was flippy and very long.
Honestly, I feel like the best way to get good Katanas is to buy like 10 of them at once, throw them all, and keep the 5 or so that work. Sell the rest. I've found that 50% (or less) of Katanas are truly great fliers.