https://screenrant.com/that-90s-show-donna-sister-tina-mystery-fix/

One of That '70s Show's biggest plot holes pertaining to Donna's family can finally be solved in the sequel series, That '90s Show.

There has long been speculation that Tina Pinciotti left Point Place, Wisconsin to run off with Chuck Cunningham, the apparently prodigal Cunningham family son, who was from nearby Milwaukee, Wisconsin. Admittedly, a Tina Pinciotti/Chuck Cunningham romance would be the quintessential “May/December” relationship.