A long ago company I worked for that subsequently went through a couple of acquisitions still basically had one person in finance somewhere who was basically who you contacted for anything related to our defined benefit pension. I assume the bus factor wasn't literally one as there were legally required annual statements etc. but I assume there would have been some manner of chaos if this person from a no longer existing company wasn't there one day. (About 7 years ago, the benefit administration--now a responsibility of Dell's--transitioned to one of the big benefit administration companies; OI expect the person who had been handling it retired.)