Roster info after trade deadline...
The 23-man roster limit is in place from the conclusion of the preseason until 12:01 am on the day of the NHL’s Trade Deadline. After that teams are allowed to have an unlimited active roster at the NHL level, provided players are signed to one of their 50 contract slots. NHL teams are only allowed to dress a maximum of 20 players – 18 skaters and two goaltenders – for any given game, but those 20 must come from the 23-player active roster.
Both the 23-player active roster and 20-player game roster can change day-to-day and game-to-game. All changes to the team’s 23-player active roster must be cleared through the NHL’s Central Registry before the move is considered finalized (and before the player is eligible to play in a game). In most cases the clearance from Central Registry is simple and completed in a nominal time span. Changes to the 20 players on the game roster are even easier – the list is submitted to the NHL official (either referee or official scorer) by the team (usually the head coach) moments before the start of the game. Prior to submitting the list, the team can choose from any members of its 23-man active roster.
So the leafs could have 30 players sitting around that they can pick for their "23 man active roster" and then they pick their 20 man "game roster from them"