The way that George Lucas chose to tell Star Wars Skywalker Saga story forever changed the way movie franchise get made (and how stories, general get told). By beginning in the middle of the saga with A New Hope, Lucas was able to offer viewers an exciting Original Trilogy experience - but he also created some major continuity difficulties for himself, when it came time for the Star Wars Prequel Trilogy. Some of the biggest continuity snags came from Lucas' decision to incorporate key Original Trilogy characters into the Prequel Trilogy storyline - and C-3PO's origin story in the prequels is one of the biggest plotholes in the entire saga.
In a recent interview, Star Wars franchise icon Anthony Daniels addressed the issue of C-3PO's presence in the Prequels and Original Trilogy, and why Obi-Wan Kenobi doesn't seem to recognize the golden droid in A New Hope, despite having been companions with him all throughout the days of the Galactic Republic and Clone Wars. As Daniels told HuffPo, the continuity questions surrounding C-3PO's forgotten presence is not something he cares all that much about:
"I don't know, I mean.... one droid looks like another, I guess," Daniels said. "You'd have to ask a major fan that question."
At this point, There's really no discussion to be had about this particular topic: it's a plothole, pure and simple. George Lucas and Lucasfilm wanted to keep some continuity with the OT characters and merchandise when it came time for the PT, and failed to cross all the "T's" and dot all the "I's" when making sure the continuity was consistent. There's no way to go back and explain it later.
However, the great thing about the modern Star Wars era and the widening variety of content being offered to fans, is that there are now viable and enriching ways to retcon these sorts of mistakes. For instance: the upcoming Obi-Wan Kenobi series coming to Disney+ could fill in more than a few of the gaps in Obi-Wan's story - including a story arc that could retcon the plothole by having Kenobi undergo some kind of mission that would later need to be wiped from his memory - specifically the memory of C-3PO.
Star Wars has already pulled a similar "fix it" move with the story of Darth Maul, who many fans didn't want to see dead so quick after The Phantom Menace. The Clone Wars animated series (and later works) gave Maul a much bigger arc in the franchise - culminating with a duel-to-the-death with Obi-Wan, in the years before A New Hope. Comparatively, fixing C-3PO's story feels like easy lifting.
Star Wars: The Rise of Skywalker hits theaters at December 20th. The Mandalorian streams every Friday on Disney+.