HI ,
I think the attached photos should show what is known as a Merese, a blade like knop separating other knops or a bowl from a stem ,the ring around the base of a stem I believe is termed as simply a reinforcing ring , added by the gaffer if the stem to foot joint was needing a little support , this feature is most commonly seen on16th and 17th c glasses with very thin stems,why it would be on the OP's glass i have no idea .
cheers ,
Peter.