I'll just throw this out there...take it or leave it.
Bulldog guys especially will know what I'm talking about.
If I'm breeding a (supposed pure) line of dogs and I run across a certain dog that I feel will compliment (or IMPROVE) my line, but that dog perhaps is of uncertain origin (or maybe even KNOWN origin

). I breed dog anyways, and perhaps my registration papers just aren't that reflective of what just happened. To put it another way, future generations will see on those papers what I want them to see. Get my point?
If someone doesn't believe this happens, then you're far too trusting and I have some ocean front property I'd like to sell you.
Papers are only as reliable as the people behind them, and we all know that dog folks can be tricky little boogers sometimes!