How many times NHL all top seeds have been eliminated in the first round?

Question

In the 2018-19 season's playoffs, all top seed teams were eliminated in the very first round.

• The Atlantic division winners, Tampa Bay Lightnings who tied the most number of wins in a season were swept by the Columbus Blue Jackets
• The Metropolitan division winners and the defending champions, Washington Capitals lost to Carolina Hurricanes in 7 games
• The Central division winners, the Nashville Predators fell to Dallas Stars in 6 games.
• The Pacific division winners, Calgary Flames lost to Colorado Avalanche in 5 games.

Throughout the years the NHL playoffs format has changed many times, but given the current format, this is the first time all division winners are knocked out on the first round. How many times in the history of the Stanley Cup, all top seeds were eliminated in the first round of the playoffs?

Answer 1

According to the NHL themselves, it has never happened before the 2019 playoffs.

For the first time in NHL history, the top team from each conference and all division winners were eliminated in the opening round. The Carolina Hurricanes completed a first-round sweep of the division and conference champions when they defeated the Washington Capitals 4-3 in double overtime at Capital One Arena to win Game 7 of the Eastern Conference First Round.

... Washington joined the Tampa Bay Lightning (Atlantic Division, Eastern Conference, Presidents' Trophy), Nashville Predators (Central Division) and Calgary Flames (Pacific Division, Western Conference) among teams eliminated in the first round.