Geyer

I have only played one Carl Geyer, and saw a second in person, but that's it. I have examined tons of photos, and had the opportunity to purchase a single (F w/muting valve) in playable but patched condition that will arrive Thursday or Friday. The price was good enough that if it is just a old American horn it's still not too much. Besides, the valves and flare appear to be appropriate. If this is indeed a Geyer, is there a way to date it? Did he use serial numbers?