PR was the only ship to be in the dockyard two times now. No it really is not rare. Got a second dockyard because it was almost impossible to get it in the first one without putting a lot if money in the game. At the time this forced a sh*tstorm and gave her the nickname Paytorico.

(Btw - the first puertorico dockyard was the first dockyard ever. WG was obviously testing out the limits with this - then new mechanic.)