pretty sure everything sold at Cor establishments "has COR" even Agri in Toronto has COR.
You are correct. Someone here does not understand how these things work. COR does not certify Mehadrin. None of the packages I saw locally have COR on them. COR might accept Mehadrin products in their stores. That does not mean they certify it. I checked the COR database, and Mehadrin is not on their list of companies they certify.
The Vaad here does the same thing. They put their emblem on many products even though they were never in the plants. They allow their stores to sell any product they feel comfortable with. The Vaad emblem means the Vaad is comfortable with and trust the certifier of that beef, or any other product, and they accept their certification. They do not go down to Mexico, Uruguay, or Canada or anywhere else and certify the shechita.
I once asked the Star-K how they allow Diet Pepsi on their accepted list for Pesach, and allow it to be sold in Star-K stores for Pesach, when the Star-K themselves will not certify kitniyos shenishtana. They told me "there is a big difference between accepting a product and certifying a product". cRc Chicago once told that to me with regards to certain items they allow in their cRc certified stores but would not feel comfortable certifying the item themselves. That is the way hasgachos work.
I am not saying anything for or against Mehadrin. It is under very respectable supervision. I am just saying I do not believe the COR certifies it. Regardless, we were talking about fresh beef, this is processed. It may be the same plant, or it may not be.
With regards to Agristar beef, something is going on there now. Might be political, might be real issues.
https://crownheights.info/chabad-news/857147/breaking-chk-yanks-hechsher-from-agristar-meats-puts-shor-habor-in-limbo/
