The list of formations I quoted, was from autumn 1991, where one rake included a BSO (based on the carriage numbers) - by that point, based on youytube clips and photos, it seems XC rakes were still mostly 5 TFO-RFO-BG, with the 5 TFO-Mk1 diner-BFK rakes having been discontinued when more HSTs came into use by XC, BSOs not becoming common in XC rakes until 1993ish (possibly after BSOs were freed up with the removal of seating from most anglo-scottish sleeper trains)?