He always had it in the sense that yes, one leg was silver in the 1977 release of Star Wars. In-universe, he didn't always have it, going through a couple different looks over the course of the prequels; he acquired the silver leg sometime between Revenge of the Sith and A New Hope.
However, in Star Wars: A New Hope, C-3PO appears with one silver leg, and continued to sport that particular look through Star Wars: The Empire Strikes Back and Star Wars: Return of the Jedi. Once the sequel trilogy arrived, C-3PO's silver leg was fixed and instead he was given a red arm, which was also fixed later on.
And also, in the desert, it reflected the gold of the sand." As a result, his leg often appeared like a much dirtier shade of gold while on Luke Skywalker's home of Tatooine rather than the pristine shade of chromed silver that was actually present.
During the Clone Wars, C-3PO would serve Senator Padmé Amidala, the spouse of Anakin Skywalker, and was given a shiny gold-colored plating to better suit his new role.
In the original Star Wars trilogy, C-3PO changed from silver to gold after successfully navigating an asteroid field with odds of 3720 to 1, unlocking the gold skin.
They aren't abbreviations — they're model and serial numbers. R2 is a second generation R-series astromech, serial number D2. * And C-3PO is a C-series protocol droid with the serial number 3PO. *And likely several more numbers that get dropped for the sake of time.
Unbeknownst to me and to many people I've consulted since I made this discovery, C-3PO had a mismatched limb through the entire original Star Wars trilogy. C-3PO has a silver leg — the right one, below the shin. He keeps the silver leg all through A New Hope and still has it in The Empire Strikes Back.
Darth Vader's true identity as Anakin Skywalker was a highly guarded secret, known only to a select few individuals including Palpatine, Obi-Wan Kenobi, Luke, Han, Leia, R2-D2, C-3PO, Master Yoda, Bail Organa, Ahsoka Tano, Darth Maul, Grand Moff Tarkin, Grand Admiral Thrawn, Jocasta Nu, Ferren Barr, Verla, Reva, ...
Initially not a science fiction fan, theatre actor Anthony Daniels was persuaded by his agent to meet George Lucas for the casting of C-3PO in Star Wars: Episode IV - A New Hope (1977). He went on to perform the character, both his voice and body in the suit, for all the episodic Star Wars films produced.
Anthony Daniels portrays C-3PO in all the Skywalker Saga films and the standalone film Rogue One. Daniels also voices the character in the animated film The Clone Wars. In addition to the films, C-3PO has appeared in television series, novels, comic books, and video games.
Given that he has been present in some of the galaxy's most important events and has met characters like Luke, Leia, and Anakin, C-3PO has had his memory wiped a total of three times through the Skywalker saga and The Clone Wars, but why?
C-3PO boasted sound wiring, as well as a standard protocol droid verbobrain and communicator module, but Skywalker could not afford even the simplest of droid coverings, and as such, left the droid's wiring exposed. C-3PO's salvaged nature imbued special qualities in him that were absent from other protocol droids.
He always had it in the sense that yes, one leg was silver in the 1977 release of Star Wars. In-universe, he didn't always have it, going through a couple different looks over the course of the prequels; he acquired the silver leg sometime between Revenge of the Sith and A New Hope.
As evidenced in the world of Star Wars, the galaxy is chock full of 3PO series protocol droids, making the odds of C-3PO being the same droid that worked on the farm decades ago incredibly slim. Owen could have easily assumed that these were two different protocol droids if he didn't put much thought into it.
C-3PO is a droid. "He" is only even a "he" because someone opted to give him and leave him with a male voice. He's a protocol droid, not a sex toy, so he does not appear to have any sort of sexual functions at all.
R2-D2 was present when Padmé gave birth to Leia and Luke, so he knew Luke was Anakin's son – but what he didn't know was that Anakin became Darth Vader. In addition to that, Anakin's fall was surely a painful event in R2-D2's life, one that he definitely wouldn't like to remember or even talk about.
As has been noted in several instances, Artoo has never had a full memory wipe, enabling him to retain his recollections of everything he saw and heard over the decades. This includes his first meeting with Padme Amidala, a nine-year-old Anakin Skywalker, and C-3PO himself during the events of The Phantom Menace.
R2-D2, sometimes spelled Artoo-Detoo and often referred to as Artoo, was an R2-series astromech droid manufactured by Industrial Automaton prior to 32 BBY, who would participate in major galactic events for nearly two centuries alongside the Skywalker family.
In The Phantom Menace, Queen Amidala owns R2-D2, as the astromech is on her ship. C-3PO was built by Anakin Skywalker, but he built the droid for his mother, Shmi Skywalker, and he leaves the protocol droid in her care when he leaves Tatooine.
