They're only for current subscribers, and there's no way to go back and get past rewards once you've subbed. Some details on what Preferred players get: this Support article and the comparison grid.

Note that this is separate from the credit escrow — any credits you gain while you have more than 200k (as F2P) are given back to you if you sub.

Yes, some rewards are only for subs. See this for the rationale.

They're only for current subscribers, and there's no way to go back and get past rewards once you've subbed. Some details on what Preferred players get: this Support article and the comparison grid.

Note that this is separate from the credit escrow — any credits you gain while you have more than 200k (as F2P) are given back to you if you sub.