I could probably add them up, but I'm the type who gets distracted half way through and has to start over again.
I bet it is 3-400 with one or zero posts or has never logged in after joining.
I have 15 folks now who never even answered my vetting questions I sent them after registering. Some folks might use a new email address just for this site and never check back for emails so they never answer my emailed questions. Maybe they get offended by the questions. I think it's been about 50 since I started asking those 3 questions. Just my idea.
I had a webmaster who convinced me that members who didn't post for 2 years should be deleted for security reasons. I did that for a short time but felt it was wrong and not necessary. I think a lot of people join to show support but don't really care to join in the conversation which is fine by me.
I even got a donation from a person who never joined, but just likes the website. That was nice.