jooster's comment says that if you broadcast a transaction to the network and it doesn't confirm, it might confirm any time in the future - which is true. You n

jooster's comment says that if you broadcast a transaction to the network and it doesn't confirm, it might confirm any time in the future - which is true. You need to assume that any of the transactions you issue will confirm - e.g. if you issue two with differing fees, you don't know which one will confirm until it happens. But once one is confirmed, all other transactions that spend the same coins can no longer be mined. So I think both comments are right, we just interpreted your question differently.