I was at SJU yesterday and I saw a few private A/C, two of which were 737s! I saw the first one was a 73G, probably the BBJ, but couldn't get a rego. The second one's registration was N977UA. I figure it was an ex 732 from UA but I am surprised that it still has the same registration. The ex UA bird was at gate 27 or something - right next to NK and CO. Was this scheduled to fill in for NK (Spirit)?