Taking out the discussion of whether he should go back to the WHL (I think he has more to prove), I think I actually came up with an explanation for why that first year wouldn't be considered a full season. Yager did play in 24 of 24 games that year, but Moose Jaw's first game that year was on March 12th in 2021. Yager was already 16 at that point. The reason I don't think the WHL would allow that to be extrapolated to a full season is because Yager wasn't granted exceptional status in that year, meaning he wouldn't have been allowed to play as a 15 year old.
I think Yager's situation is more akin to the 16 year old prospects who get in a couple of games at the end of a season in juniors, which never count as a full season in the WHL. However, since Yager turned 16 in January of that year and games didn't start until March, he was just able to play in all 24 games. If you look at 1st rounders in the WHL, it's fairly common to find guys who got cups of coffee at the end of their junior seasons as a 16 year old. Looking at the 2020 draft, all of Quinn (8 games in 2017-2018), Guhle (8 games in 2017-2018), Jarvis (11 games in 2017-2018) and Neighbors (11 games in 2017-2018) all got these few games as 16 year old players in the CHL. Yager just played in more because the WHL had a bunch of games late in that year due to COVID.
That's why the Wright situation isn't applicable to Yager, Wright was granted exceptional status and was eligible to accrue that full year at age 15. If Yager was born in December instead of January, he would have been viewed as 16 in that first WHL year (since age seems to be determined based on age on December 31st) so he would have accrued a full season for that year.