So, the real deal on renewing CORE positions is that if they really want to, they can choose to not renew you after the temporary appointment ends. However, (and this is a really huge however), when they choose to not renew a CORE, they're not just saying, "lissable just isn't what we need in this role." When they decide to not renew a CORE, what they're really saying is, "we don't need this PIN (position) anymore." So, when they choose to not renew a CORE, they not only lose the person in the position, they lose the PIN, and HR doesn't give them a replacement for it.

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So, while, in theory, it's easy to get rid of a CORE at the end of the NTE period, in practice, it almost never happens, because no one wants to give up a PIN when it's so hard to get new ones.