Difference is they are not over agers
Are you inferring that Dufour's very successful MC season took place at the end of a long QMJHL career (which would be fine as it did) or that Dufour was drafted as an overager (which would be incorrect as he was drafted in his first year of eligibility)?
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Interestingly, the Islanders currently only have 14 properties that are listed as unsigned.
That list includes Iskhakov (KHL), Gill (signed to an AHL-only contract), and Aleksi Malinen, a strong-skating defenseman who quit ice hockey after last season (where have we heard that before?).
I'm not sure about all the new NCAA rules, but Berg is the "senior" prospect on the list as he's in his 4th year of eligibility. Up until the pandemic, that would have meant that he'd have to be signed by August 15th. I don't see any reason he can't add on another year of college hockey.
Of the remaining players, Gidlöf, Gamzin, and Good Bogg (basically a non-prospect - currently doing a whole lot of nothing in Sweden's 3rd league) are in Europe and do not yet need to be signed, Veilleux is in the USHL and first headed to college, and the rest are all playing college hockey (Nelson, Finley, Eiserman, Bednarik, and Schulz).
It's very possible that any number of these players could already be signed this summer but it's looking like the team doesn't yet have to make a decision on, well, any of them.