The X87/88 were moved from Haymarket to Eldon Square for a few reasons. Obviously, it meant that it went from the same bus station as the X77/78/79. I believe congestion in Haymarket bus station was also a factor. Of course, now all the Ponteland Road expresses now serve the bus station which makes more sense.

The X47 was originally introduced with the support of a government grant. It replaced a far less frequent 47 if I remember correctly.