"- In EP4 ObiWan says he doesn't remember ever having owned a Droid, in EP1 or 2, he owns one ... (oki, he might have lied to Luke ...)"
Ask Obi-wan if he has a receipt.
Besides, throughout the PT, R2 belongs to Padme, and 3PO belongs to Anakin - until they are both given to Bail Organa.
"- More arguable: In EP4 ObiWan tells Luke that Vador has tracked and assassinated all Jedi Knights, but watching EP3 you see almost all Jedis have been killed by the republic commandos, Vador killed the ones in the Jedi Temple and didn't actually "track" any Jedi. Maybe has he tracked some Jedis after EP3 ... but watching the movie you really have the feeling the Jedis are already all dead."
We only see a handful killed onscreen, and the whole reason for Obi-wan and Yoda to return to the Jedi Temple is to change the "Return Home" beacon, to keep any left over Jedi from returning to Coruscant. These are presumably the Jedi that Vader later seeks down and kills (in between ROTS and ANH.)
"Dark Vador"
I want that to be my new username - LOL.