Per the current Collective Bargaining Agreement, every NHL team is permitted to have 50 players under contract in their entire organization; including players that are not with the parent club.
This was the reason that the Flyers were required to include Jon Kalinski in the trade for Pavel Kubina. The Flyers already had 50 contracts, so they could not acquire Kubina without shedding a contract first.
However, it is possible to have more than 50 players under contract if you have what are called “slide contracts,” as they do not count towards the 50-contract limit.
In the event that an 18 year old or 19 year old Player signs an SPC with a Club but does not play at least ten (10) NHL Games in the first season under that SPC, the term of his SPC and his number of years in the Entry Level System shall be extended for a period of one (1) year - CBA Section 9.1(d)
This typically applies to Junior players, who sign their contracts at 18 years old, but return to Juniors until they either a) make the NHL or b) are old enough for the AHL. Once such a player plays in their 10th NHL game, they effectively “burn” a year off of their contract, and count towards the 50 contract limit.
We saw an example of this with the Rangers’ Chris Kreider, who jumped from Boston College into the NHL and promptly burned up a year with the Blueshirts’ long playoff run.
If the player does not play in 10 games, the contract is extended for an additional season; which effectively means the the three-year entry-level contract that was signed does not lose a year.
This is why you may recall the discussion about whether or not to send a player back to Junior before they play in their 10th game. Sean Couturier and Luca Sbisa are recent examples of this. Ultimately, they both played beyond 10 games, and their contracts did not slide.
You can view the Flyers current Reserve List here. Players with slide contracts are denoted with an “SR”. Nick Cousins and Derek Mathers would currently qualify; and being that it is unlikely either of them would make the Flyers, their contracts will more than likely slide.