DAR records from a couple generations ago are sometimes slipshod. I also had some folks join on an ancestor of mine that has since been discredited. No more memberships can be based on that individual.
Today, with digital records, etc. DAR is a lot more picky. You can no longer prove descendency based on county book sketches, etc. They want to see wills and other court documents regarding birth, marriage, death; bibles; sometimes graves, but they want to see something set in stone as it were. Many of these older family lines have been discredited.
Speaking of DAR, I have my grandmother's letter of acceptance from the local group but cannot find her in any of their records or those stacks of blue books at the library. It doesn't matter because I've never been interested in joining and there is at least one more she might not have known about. I don't think I could prove any of the rev war ones w/o professional help and then maybe not even then.
Some of those older birth, marriage and death records no longer exist anywhere. Some never existed at all except by word of mouth or have been lost. Even graves and stones are lost. I do think I could pick up a few more proofs and links if I were free to travel and do the arduous hunting.
I have to chuckle though. Even the peerage books, like I concluded with a relative who was asking about our lines, "one indiscretion and the whole thing falls apart."