I was a country instructor when the BFR came in, 1982-3?
There were PPLs with licences for many years with no oversight, some great, some not.
I finished many in an hour or so, trying to cover items the pilot would get the most out of as a learning experience, depending on the way they used their licence. Although you may not be able to "fail" a BFR it is certainly possible to not complete one.
One guy, with his own aircraft, was very poor in all respects. He had his own aircraft on a private strip for maybe 20 years with no oversight at all.
After a quick flight I was able to tell him where I felt he was at and work out a plan to get him up to scratch. I understand he gave up flying eventually having never flown with me again, a good outcome in that case.
As a motor mechanic He did all his aircraft work and found a tame Lame somewhere to sign it out, definitely the worst GA aircraft I ever flew!
These days with pilots doing the review every two years it should be easier!