The outward angle of the rim is the plus mold and is not the difference between 11x and 12x teebirds. Also I'd be quite surprised to find out that they didn't have CFR runs teebirds when climo was an 11x champion, but I'm just speculating there. So I'd guess an 11x CFR Teebird is quite possible.
If its a CFR and doesn't have the stock stamp it may be difficult to tell if its actually an 11x teebird. You can check the tooling on the back of the disc and if the abbreviation for california is abbreviated "CAL" and not "CA" its an 11x. If its "CA" it may still be an 11x, however all 12x are also tooled this way. If it does have the stock stamp but its wiped or worn look at it under a light under different angles and obviously look for the "11x/12x world champion"
Most 11x Teebirds are desirable because they are flat, very HSS with little to no turn compared to later run domey teebirds. If you can compare it to a new run teebird and it seems to have a flatter/less domey flight plate it may be a good indication of whether its an 11x or not. The 11x moniker is not actually what is desirable, its the flight, and the 11x is a good indicator that a disc was molded at a time when they came out flat and stable to overstable.
Hope this helps!
EDIT: Bonus if the CFR has a tourney stamp with the year dated on it. Would be easy to tell then (He won his 12th in '06, so I'd assume it would have to be stamped as then or earlier)
There is a section on dgcr of "what is this disc worth" where you would be able to ask about it. Just post a pic and ask your question. I DO know there are two distinct types of 11x tbirds, with one being more overstable than the other. The pearly flat tops are the most sought after but the are the more clear tops which tend to be more overstable. CFR's WERE done with 11x which I know for a fact, just need to ask around. Again, a picture would go a long way.
11x Teebirds were molded with both the CAL marking and CA marking. I have a CA molded Teebird in my possesion and it is definitely more overstable then any 12x Teebird I've ever thrown even at a scant 154 grams.
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