Yeah, those caches never being logged online is embarrassing. Despite my proximity, I'll bet I've only been in the London area twice in my whole life. No, I'll not be doing "The London Loop", even though one of them was named after me.
Someone recently logged one of 3 opencaches placed in Rhode Island in 2011. Now only one is unfound. In my experience around Buffalo, N.Y., which is one of our highest density areas, I've often found non-online loggers in the logbooks. Too many times to think it's Geocachers who just happen to stumble on an unknown to them cache.
Best of luck with the other two. I see one is quite west of London. BTW, I too love
finding lonely alt site caches, be they ours, TC's or even Navicaches.