Austrian Parcel Post Receipts - Istanbul or Constantinople?

These are some of my favorite pieces.  These vary in date, but display several stamps from late in the Franz Joseph reign.  All three are to Istanbul, but it is curious that some of them have both “Istanbul” and “Constantinople” written on them.  I’m not sure exactly when the terminology changed, but I am guessing it is around this time.  The name was formally changed in 1930, but these would indicate that some usage began prior to that date as these three are all from 1917.  The three examples below all indicate different usages.

Nov 17, 1917 sent to Constantinople — date received is unclear.  Rate of 2 kronen 95 heller.

Nov 20, 1917 sent to Constantinople (with “Istanbul” listed below) — date received is unclear. Rate of 2 kronen 95 heller.

Nov 1, 1917 send to “Constantinople-Stanbul” — date received is unclear.  Rate of 2 kronen 95 heller.