You need to check players' Elite Prospects pages. They show their stats of almost all of their previous levels. Some going all the way back to midget-AAA.
HockeyDB only shows stats of more main leagues. Last year, Merrill played at a prep high school (same school Struble played in before he was drafted). He played 25 games there putting up 18 goals and 37 pts. And he played 2 games in the USHL after his high school season was over.
Since HockeyDB doesn't list the high school stats, all they have listed for Merrill are his 2 USHL games. But on Elite Prospects, you'll get his stats dating back to the 2020-21 season, going back to his 14-15 year old season.