Keeping samples for eight years will have no effect if players work out ways of blood doping while keeping haematocrit within range by microdosing. The traces disappear quickly and completely so glow time is too short to be picked up. If you accept Ashendon's thesis on Contador, what the Spanish cyclist was actually doing was blood doping rather than doping with the clenbuterol that was found in trace quantity only in his system.
The ITF will need some good experts of Ashendon's calibre to back the bio-passport up. And where's the money coming from to do all this? Any prize money confiscated from cheats ought by right to go straight into the tennis anti-doping pot. Consideration should also be given to an additional financial sanction, heavy enough so the message goes out loud and clear that doping does not pay and will cost you dearly. At the moment doping pays very nicely, thank you very much.