Right, but in principle KLM could say after six months when you've done your qualifying flying that all you need to do to actually execute the "transfer" you signed up for is to send them your current FF card together with a confirmation that you have terminated your account with your old airline.

It would be really stupid of them, and I'm not saying they will do it, but the fact that other airlines will not terminate your account at the request of KLM doesn't necessarily mean that you will get the FD points without giving up your currents ones.

Again, I'm not saying this will happen, just that your conclusion is not waterproof.