I am going off my memory here and may be wrong but:
The 8 was Stanley - Castleside initially.
The X8 was Sunderland - Stanley.
The X2 was replaced by the 8.
The 8 replaced the X8 and stopped running to Castleside.
RE: Go North East: Latest News & Discussion - February 2016
'Illegitimis non carborundum'