I think the simplest way to say it is that there are 4.3 billion valid safecoin addresses. That address space limits the number of potential safecoins. The safecoin itself is simply a structured-data object with a valid address. There will almost certainly never be that many safecoins in existence at any one time.
Safecoins are created (freshly PUT to the network) in the farming process and destroyed (erased) when used to purchase resources from the network. The address space that that erased coin had occupied is then available to have a fresh coin (structured data object) minted with that valid safecoin address in response to a successful farming request.
So safecoins are both recycled and deleted. The limit is in the valid address space. Once a structured data object has been created by the network at a valid address, no other safecoin can be created there. Once it is deleted, that address can be used again.
“Recycled” is a very good term for it, I think, but perhaps saying that safecoins are “phoenixed” would be better. 
Hope this helps.
See also, New Wiki entry: Safecoin Issuance and Distribution