Airclues Meikleour is correct although you have the wrong dates.
It was the joint seniority list made at the creation of BA in 76?
My course which joined around the time the vanguard made a smoking hole near Ghent was the first course after the last Hamble/Oxford/Perth cadet joined BOAC, which was supposed to be the demarcation line for cross bidding. Unfortunately our BALPA rep was as desperate as a lot of others to leave BEA which had a dreadful accident rate and changed the date by two years so that he got onto the jumbo. There was a proviso that no BEA copilot would be senior to any BOAC pilot..iirc wrt to bid lists.
The guy did me a favour as I got the iron duck.
It wasn't unknown of BALPA REPs as we had a famous scumbag who sold us out after papa India and the next day joined management ..known by the bomber boys as that #### ####ing..inventor of the silent cockpit.
I had two of my course mates, one chopped and the second ex court line, victims of BALPA and the Dan Air merger which was to be done on seniority but at the last minute was done on those on the bus. One lost one won.