8 Star Wars Prequel Moments George Lucas Planned Way Back In 1977
4. C-3PO Had His Memory Wiped
"I believe Artoo had his memory erased several times, but I'm sure that horrible fate never befell me." - C-3PO
Even with CGI Jabba and visual continuity issues smoothed over, A New Hope still presents some unavoidable plot holes, with characters keeping schtum on key issues for no apparent reason other than plot necessity.
Not much can be done about wise exposition-giver Ben, but Lucas had a good stab at explaining blabber-mouth C-3PO not knowing who Vader is by retroactively giving him a memory-wipe. Narratively simplistic (it's skirting very close to All My Circuits' amnesia), it does the job of tying up a loose end that was stupidly created by the prequels' lack of foresight.
However, as one of the better written excerpts from Lucas' notes reveal, 3PO was always intended to have a heavily-influenced view on the world. Talking about his relationship with R2, Lucas uses the first-person style of these notes to have some fun in suggesting, but not confirming, some less galaxy-shattering events.
Less ambiguously, the passage also explains why the Tantive IV's translator wasn't aware of the consular ship's ambassador; he was specifically programmed to not reveal any information on Leia. Although in explaining that one piece of erroneous dialogue, we get the question of why he needed a whole memory wipe in the first place.