Corporate memory comes from writing stuff down in manuals not simply relying on somebody remembering. That somebody can fall under a bus, can be promoted to post and a location where he is effectively unavailable or may retire. Relying on gurus is all very 1960s but it isn't the way a modern business can run. I suspect that the government, when it decided to electrify the GMWL, actually thought that NR did have the records
I don't know whether BR did record what they did (and why) and RT or NR threw it all away, but I do hope, as a taxpayer, that NR do recording (what, where, why and when) for the future.
Regards