[...]

The announcement of Robert Picardo returning to Star Trek as Voyager's Emergency Medical Hologram immediately brought about as much speculation as it did excitement. While it's since been confirmed that Picardo will be playing Voyager's "main" Doctor in Starfleet Academy, the show in which he originated the role accidentally made it possible for a compelling alternative. In Star Trek: Voyager Season 4, Episode 23, "Living Witness," Picardo played a version of the Doctor who had been extracted from his ship's backup module, which had been recovered on an alien world in the 31st century. He had been deactivated since the 24th century.

Near the end of "Living Witness," the episode's voiceover revealed that the Backup Doctor remained on the planet for a little while, but eventually set off to try and reach Earth, even though everyone aboard the USS Voyager would have been long dead by that point. If this version of Picardo's character did end up getting back to the human homeworld, his arrival would likely align fortuitously well with the 32nd century, when Star Trek: Starfleet Academy is set. So, with the "main" Doctor having served in Starfleet for centuries, the upcoming show could have the "Living Witness" version enter the fray, lacking almost all the memories and experiences of his counterpart, making them both very different characters. [...]