Unless some of the sarsens (the big upstanding stones) have since been removed from the site, the ring appears to have been left incomplete.
to this one:
It was thought the ring might have been left incomplete, but an exceptionally dry summer in 2013 revealed patches of parched grass which may correspond to the location of removed sarsens.
It's should be old news really, but it was only just reported in the Guardian. I'm completely fascinated by the archaeology we can do just by looking at the shades of disappeared structures expressed as soil colour, fertility, water retention. Even more amazing is the way it only 'works' at certain seasons and under certain conditions. Just like real magic!
Despite Wikipedia's reputation, I always feel the same way when I edit one of its articles: terrified lest I make an error, amused to discover the Stonehenge article is on partial lockdown (though I seem to have some ill-deserved regular editor status), annoyed at the hideous interface, and wry about the fact that my reference was longer than the sentence it justified.