Most Spiegel checkered buttstocks showed up from 377,xxx and above (Jaaack's EG is 361,xxx). Even if you found an earlier Spiegel with checkering (and I have notes on at least one), you can't rule out that it wasn't just a receiver that got finished 6 months or a year late.

So Jaaack's is early 1937
Checkered Speigel's are mid 1938


Checkered forearms on Spiegel's happened about the same time as checkered EG's.

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