I don't remember there ever being 4 diagrams every day. There may have been "up to 4" diagrams but never 5.
The intention was however to introduce a 4 set service once the power door conversions were finished, along with various timetable changes that were consulted on around 2017, but that's been delayed.
There were never 5 in use every day but I do remember 4 at some point around 2009 but this only lasted about a year or so before the reduction to the current level. I seem to remember the reason stated for the reduction was the cost of running the
HSTs▸ .
I have just found a post on another forum from 2009 which quotes the diagrams which were listed on the 125 Group website:
17 May 2009 – 12 December 2009
MONDAYS TO FRIDAYS
XC801 1V44 0600 LDS-PLY» , 1S51 1221 PLY-GLC▸ , 5S51 22+40 GLC-EC.
XC802 5V39 04+41 EC-DEE, 1V54 0632 DEE-PLY, 1E73 1721 PLY-LDS.
XC803 5V46 05+14 NL-YRK, 1V46 0632 YRK-PLY, 1S55 1321 PLY-EDB.
XC804 1V50 0608 EDB-PLY, 1E63 15:21 PLY-LDS.