When upgrading ships, do I retain access to my previous ship in the PTU?

I'm mainly asking so that, if I upgrade my ship to a concept ship (if we can even do that), that I still have a ship to fly in the PU.

I upgraded my Aurora to a Connie a while ago, and I still have access to the Aurora (which I assume is only until the game comes out, then the Aurora will be removed). Does that mean that if I upgrade my Aurora to Connie upgrade to, let's say, a 600i, I'll keep the Aurora and connie? Or, will I just keep the Connie? Or the Aurora? I'm a little confused as to how this works.

The thing is, I just don't want to be without a ship that can transport vehicles in 3.0 while everyone waits for the 600i to be completed.

Edit; I had said PTU and meant PU. sorry for the confusion.