To my eye, the Lemond bike looks somewhat large for Greg. At very least the seller should indicate the true measured frame size and not only indicate "Greg Lemond's size". I own one of the bikes that Roberto Conti rode in 2000. The bike carries the original personalized decals, I have a confirmation from De Rosa of teh serial number correlation and I have a note from Conti himself. So, yes you can "prove" provenance.