[LanPB01]

I guess you don't think Obi-Wan saw C3PO at all during Attack of the Clones or Revenge of the Sith.

[Buggman]

No, just that C-3PO wouldn't necessarily stand out in his mind. If you'll look back on human/droid interactions through the movies, you'll notice that humans basically consider droids to be talking appliances, not people in their own right. Remember how blithely Luke said, "He'll be alright," when R2D2 was nearly destroyed in EpIV?

That being the case, why would one protocol and one astromech droid make much of an impression on Kenobi? If you once owned a Maytag refrigerator, and ran across another of the same model years later, would you assume them to be the same?