The NHL-SHL transfer agreement didn't apply to Dahlen. He spent a year in the AHL, underperformed, and was sent back to Timrå to regain his confidence. He dominated the Allsvenskan but a global pandemic broke out and ended the season early.
The NHL then didn't get a season going on time, while the Allsvenskan started playing in September, so Dahlen stayed in Timrå for another year because there wasn't yet an NHL or AHL season even scheduled (that didn't happen until late December 2020). Dahlen stayed in Sweden an extra year because his choices at the time were play in Sweden, or sit around doing nothing while waiting to see if there even would be a season in North America.
He dominated the Allsvenskan again, led Timrå back to the SHL, and then came over for a year where he was decent enough but lacked physical stamina and wasn't productive enough offensively to change minds, so he went back to Sweden when we didn't qualify him. He's had one good year and one decent but disappointing year there so far.
Dahlen was turning 22 the year we sent him back to Timrå, and was past the age that the then-transfer agreement specified (it was then 21 years old, which is why he was playing in Utica). The agreement now sets the age at 24 (and of course the Swedish team can allow the player to play in the AHL).