Drake Rodger as John Winchester, Meg Donnelly as Mary Campbell, and Jensen Ackles as the voice of Dean, The Winchesters chronicles Sam and Dean's parents in the years before marriage, kids, and Lucifer.
As soon as The Winchesters was announced, however, fans questioned how the prequel could slot into Supernatural's timeline. The initial synopsis teased young John Winchester as a hunter, but only Mary should know about the paranormal. More recent details have only worsened those continuity concerns. John and Mary's ages suggest The Winchesters will take place shortly after the deal with Azazel (from Supernatural season 4's "In The Beginning"), but Mary's synopsis retcons her relationship with John by claiming they've only just met, rather than being almost engaged. Her background ignores Samuel Campbell's death by saying he "disappeared," while John's character description confirms that post-Vietnam hunter career.
It's possible The Winchesters will simply break canon for the sake of telling a more interesting story. It's also possible these early synopses won't accurately reflect the finished product. Assuming the details released thus far hold true, however, can The Winchesters carry on without going wayward?
The Winchesters Takes Place In A Parallel Universe
The easiest solution to The Winchesters' continuity woes is shifting the narrative to an alternate universe. Supernatural has done the hard work here, confirming the existence of countless parallel realities - most of which God created seeking various ways to make Sam and Dean murder each other. There's even a world where John Winchester doesn't die, becoming CEO of HunterCorp while his two sons turn into hilariously spoiled hipsters. Given the broad spectrum of different universes already on the board, there's bound to be a timeline where John became a hunter early, didn't begin dating Mary until later, and where the Azazel deal plays out slightly differently.
A parallel universe setting gives The Winchesters a clean slate to launch from, completely removing all limitations on story and character. The prequel can use whomever it likes however it wishes - all without worrying about how those changes adhere to established lore. For the audience's part, they'll get to watch a prequel series without knowing how the story ends, giving The Winchesters a unique selling point - a prequel that's still unwritten. And since multiverse madness is all the rage right now, a parallel universe John & Mary Winchester tale would be perfectly en vogue.
The Winchesters Involves Time Travel
If not an alternate reality, how about time travel? As demonstrated by John Winchester's accidental return in season 14, Supernatural follows the Back to the Future rule book of changing history, where one crushed butterfly in the past completely rewrites the present. Unfortunately for Sam and Dean, Supernatural makes travelling in time a whole lot easier than building a flux capacitor and stealing plutonium. It only takes a single spell, a misguided wish, or a disgruntled archangel to zip backward and make a single tweak. Suddenly, Dean Winchester is a vegan and Sam has a mohawk. Perhaps, for example, some misguided time-hopper travels back to the Vietnam War, where they meet a young John Winchester and tell him the truth about monsters, completely altering his destined path. The Winchesters could then follow this alternate road, ending when John and Mary realize they have no choice but to course-correct.
Turning The Winchesters into a time travel story holds one major advantage over the parallel universe option - everything takes place within the original, authentic Supernatural universe. The cost would only come at the very end when the timeline has to be reset for the sake of protecting continuity. Helpfully, Rob Benedict (God) and Richard Speight Jr. (Gabriel) - arguably the two characters most likely to fiddle with history - have both declared themselves available for The Winchesters.
An Angel Wipes John & Mary's Memories
In Supernatural season 5's "The Song Remains The Same," Sam and Dean once again visit their young parents in the past. This time, John actually discovers his wife's paranormal secret, and helps his future sons against rogue angel Anna Milton. John's early knowledge of monsters and angels threatened to completely alter his future... until Michael strolled in and wiped John's memory, ensuring his timeline played out as intended. Could something similar transpire in The Winchesters?
If the Supernatural prequel begins shortly after Azazel's deal, some angelic force could descend from the heavens and wipe Mary's memory. That would explain why she doesn't where her father suddenly vanished to, or her existing relationship with John Winchester. By the end of The Winchesters, it'd be John's turn to forget - losing all recollection of being a hunter and the existence of monsters. While spamming an angel's ability to afflict amnesia could explain how The Winchesters fits alongside Supernatural canon, using the device again would risk feeling cheap - especially after the main show already went there.
Dean Winchester Is Telling A "What If...?" Story
Though story details for The Winchesters remain vague at present, Jensen Ackles reprises his famous role as Dean to narrate John and Mary's past adventures. Given how little Dean actually knows about their past (each Supernatural time travel episode yielded more secrets he wasn't aware of), this is a curious addition to the show's premise. Rather than using Dean merely as a star-powered framing device, is there a deeper reason he's narrating the story">story where John and Mary are allowed to make the world a better place through hunting, but aren't condemned by Azazel or chased by their destiny.
While a Winchester What If...? gives the same narrative freedom a parallel universe would, it lacks weight and consequences. Dean is hardly going to spin a yarn where his parents are placed in any serious danger, after all...
The Winchesters Reboots Supernatural
The most unlikely route for The Winchesters (albeit still not impossible) is a full reboot of Supernatural's franchise. Aside from the detached voice of Jensen Ackles, there's nothing concrete to connect the two shows. John and Mary are portrayed by different actors, the creative team behind-the-scenes has switched, and at the time of writing, no former Supernatural actors are confirmed for onscreen roles. Every few years, the Lost is never far away from reboot rumors.
Supernatural could go the same way, but rather than simply restarting Sam and Dean Winchester's story, we begin in the 1970s with John and Mary. Audience reaction to The Winchesters rebooting Supernatural would almost certainly skew negative, but if the prequel proved successful, there'd at least be room to continue the story indefinitely.