not to sure but from what I read it was a very small and late bann so IMO only numbers 1-6 would apply but it is only an opinion but hay get a number 1 and you can't be wrong :blush:
Yes, as Paul says, this was a relatively late Bann (raised in 1941). . I don't have any Gefolgschaft-level lists for Bann 491 so can't give you a maximum valid number but as with any shoulder strap, if you go for a low button number you can't really go wrong.
Button numbers only really become a problem if you're putting a uniform together because then you have to take account of the fact that Gefolgschaft numbers related to the Schar number which in turn related to an age-group (Schar 4 was for 14 year old boys, Schar 2 for 15 year old boys etc). With that in mind you'd have to be careful with achievement badges/ranks etc.