Given Guess Who has now concluded, once again through somewhere other than the US, I thought it might be interesting to do a detailed rundown of how many episodes in the past three series aired in other countries before the United States.
21 episodes of Scooby-Doo! Mystery Incorporated aired in Canada and the UK before they aired in the United States.
The last 12 episodes of season 1 aired on Teletoon in Canada about two months before they did in the US. "The Wild Brood" (episode 15) aired March 15, 2011 on Teletoon Canada. Episodes 16-18 continued to air every day that week through March 18, 2011. "Nightfright" (episode 19) aired on March 24, 2011. Beginning April 30, 2011 with "The Siren's Song," new episodes aired every Saturday until the season concluded with "All Fear the Freak" on June 11, 2011. Note that episode 14, "Mystery Solvers Club State Finals" would have also technically aired in Canada before it did in the US, had Cartoon Network not forgotten to notify iTunes and Amazon after their sudden airdate switch from January 31, 2011 to May 3, 2011. Due to the lack of notification, iTunes and Amazon posted the episode the next day for purchase, despite the fact that the episode had not aired, but they quickly took it down the next day.
After Cartoon Network accidentally messed up and posted the season 2 premiere on their own site in error on March 30, 2012 (they meant to post the season 1 premiere, which is what quickly replaced the season 2 premiere once the error was discovered the following Monday), the UK aired four more episodes (episodes 28-31) of season 2 between June 3-6, 2012, the US finally caught up and aired episodes 32-41 before any other country. Another lengthy hiatus occurred after episode 41, which allowed Teletoon Canada to slip in airing episodes 42-45 between every Sunday March 3, 2013 and March 24, 2013 before they did in the US. Episodes 46-52 aired in the US first.
Moving to Be Cool, Scooby-Doo!, a few episodes of season 1 aired elsewhere before their US airings. Episode 15, "If You Can't Scooby-Doo the Time, Don't Scooby-Doo the Crime," aired in the UK on October 27, 2015, whereas the US aired the episode on February 6, 2016. Starting with episode 22, "I Scooby Dooby Do," every single episode aired in another country before the US airing, in many cases over 6 months earlier. The UK aired episode 22 first in May 2016, followed by Canada airing episodes 23-41 (episodes 23-26 were aired in August 2016, episodes 27 and 28 were aired in April 2017, and episodes 29-41 were aired between May 28, 2017 and June 13, 2017). Ironically, Canada had finished airing through season 2, episode 15 one week before season 1 finally concluded in the US on June 20, 2017. Episodes 42-49 aired in Australia in July 2017, while the two-part finale aired September 14 and 15, 2017, and the episode comprised of two shorts aired November 13, 2017 in the UK. This adds up to 32 episodes aired elsewhere long before they aired in the US.
Finally, with Scooby-Doo and Guess Who?, while the first 13 episodes aired in the states before anywhere else, "The Nightmare Ghost of Psychic U!" aired in the UK in October 2019, 9 months before the US. Boomerang UK got episodes 15-18 in February 2020, and HBO Max in Spain got the rest of the season with the exception of Bill Nye and Neil deGrasse Tyson (possibly due to an active sexual harassment investigation against Neil at the time). On May 9, 2020, "Space Station Scooby" aired in Australia. A season 2 episode, "Lost Soles of Jungle River!" aired in the UK on July 25, 2020. For once, the US aired the first half of season 2 before anywhere else on October 1, 2020, as well as "Total Jeopardy!" on November 13, 2020 to honor the late Alex Trebek's memory, but they fell back into old patterns when Turkey began airing episodes 41-45 in January 2021 (they'd later air in Canada in English between March 7, 2021 and April 4, 2021). One episode did air on the Boomerang service as a publicity stunt of sorts, that being the Axl Rose episode on February 25, 2021. The final episodes aired on a special pop-up channel in Australia on April 7, 2021, and then in Canada every Sunday between May 9, 2021 and June 6, 2021. Overall, 24 episodes of Guess Who aired in other countries before they aired in the United States.
To sum it all up, of the 156 episodes from all three series, collectively, 77 episodes have aired outside the United States long before they would ever air here. This seems to be a pattern with the past three Scooby series, which is unfortunate because it would be nice if all the countries could get these episodes at approximately the same time, to save people either having to wait months (or years, in some cases) or having to watch them in other ways.