So, to elaborate a bit on this, Schneider is in the same situation as Ryan Gropp was in 2015 and the rule only applies to prospects born between Sept 16 and Dec 31.
1. The age is determined by the player's age on September 15th, as outlined in CBA article 8.10 on page 22
View attachment 382532
2. The distinction between early birthdays (9/15 - 12/31) and late birthdays (01/01 - 9/14) is outlined in 9.2(d)(i) on page 23
View attachment 382535
3. The requirement for a professional year (i.e. "burning a year") is explained in article 10.2(a)(i) on page 30
View attachment 382533
As Braden Schneider was born in 2001, and therefore will turn 20 in this calendar year, his contract will not be slide eligible at all. The easiest way to compare 2 players in this situation is to look at the 2017 NHL Draft.
Rangers drafted and signed Lias Andersson in 2017, and as a 1998 born player, 2017 was his CY19 (calendar year of his 19th birthday).
Sabres drafted Mittelstadt in 2017 and signed him in 2018. Mittelstadt was also a 1998 born player, but he signed in his CY20 (calendar year of his 20th birthday).
Therefore, Mittelstadt's entry level contract did not slide despite playing fewer than 10 games outlined in article 10.2(a)(i) because he falls under the exception in article 9.2.(d)(i)
Why did Schneider not sign? The same reason Lafrenière didn't play in the World Juniors (I still believe it was the player's choice). An entry level slide benfits the team, but the player can hit RFA status a year earlier if they play their cards right. Earlier payday for Schneider is a good incentive to not sign prior to January 1st
Ryan Gropp in 2015 signed on December 31st, resulting in his ELC sliding twice. For Gropp it meant a payout of 92,500 dollars as a signing bonus, and he was under contract until 2020, instead of hitting RFA status in 2018. Did that benefit him? I guess, since he was guaranteed a pro contract for 3 full years after finishing his junior career. He basically got paid a minimum of 70,000 5 years in a row.
Schneider might be betting on himself getting a big payday in 2023, by signing his ELC in the coming weeks and play in the AHL under the new exception
TL;DR:
A player who turns 20 (or older) in the year he signs his contract will not be eligible for an entry level slide. Schneider turns 20 years old in 2021.