Looked this up from last season...
Columbus played Tampa in Game one of the playoffs on April 10th, 2019.
A few days later, the Jackets signed Vladislav Gavrikov to his first NHL contract, after his KHL season was over. He played in two games later in the Boston - Columbus series.
Based on that fact, would believe some of these players like Romanov, would be eligible to play in the playoffs or play-ins since the regular season was declared completed.
Don't know the NHL's logic otherwise, they would seem to be changing the rules.