A short time before Sept 1919 according to this:
http://www.remingtonsociety.com/rsa/questions/FR09
EDIT: I see you got a date answer in your original post in 2011
http://www.remingtonsociety.com/forums/ ... 816#p29816
Values aren't typically assesed on this forum (I'm told), but condition really is everything.
The extra numbered barrel will add a slight premium if in COLLECTIBLE condition. If it's not in "Excellent" or better condition (or 95% or better) it's just another barrel, to me.
So, if in less than pristine condition, you have a Standard Grade Model 11 with an extra riot barrel.
That's the way I see it, anyway. Others may have a different opinion.