Originally Posted by Blue Order
Think about how bikes are dated-- most often, the advice is to check the components for date codes. So what happens when somebody buys a vintage bike, and strips it down to the frame for conversion to fixed gear? The date codes for that bike are lost forever. Then add in all the conversions that remove all trace of the bike's origin, and you have an unknown bike of unknown vintage. Nobody will ever be able to sort these bikes out. When the fixed gear crowd moves on to some other hobby, the vast majority of those bikes will be abandoned as worthless scrap.
Don't forget parting out a bike to get the maximum money will have the same effect. The frames I bought are from parted out bikes. I tried to get as many of the original parts as I could but I didn't have the means to get them all.