I have a 12" Goerz Dagor lens that I use on rare occasions. I am aware that there are a number of variations of the lens but I don't know the differences. There's a red dot, a gold dot and no dot at all. Some have a gold ring, some don't. Recently I have noticed a wide disparity in the value of these lenses.

Can someone give me cliff notes about the various versions of this lens and how to tell whether mine is one of the $100 ones or one of the $1000 ones? I'm not considering selling it at this time but it might help me decide a later date.

Thanks.