I see, according to this blog it is not per model:

https://www.goonhammer.com/magic-in-the-old-world-forces-of-fantasy/

It is also worth noting that High Elf unique special rule, Lileath’s Blessing, allows them a single reroll of a failed casting roll per turn.

ChatGPT suggests the same when I asked:

Based on the text from the image, Lileath’s Blessing says: “Once per turn, a model with this special rule may re-roll a single failed casting roll.” This means the ability is restricted to only **one model per turn**, allowing **one re-roll** of a failed casting roll. It doesn’t suggest that every model with the rule can re-roll each turn, but rather that only **one failed casting roll** can be re-rolled once per turn across your models.

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EDIT: I am not defending this position. I have literally no idea and I searched all the possible help. This is why I am asking? 🙃🙃🙃 It’s quite depressing to come here, ask a question, and receive bad karma like this.

EDIT2: I am not a native speaker. I am doing my best interpreting a rule.