Right of abode is a fact of who you are and not dependent on paperwork. And i am at a loss to understand what you mean by "it was their responsibility to assemble the requisite paperwork".
The paperwork requirement, for evidence of residence in the country in every single year post 1971, was a requirement imposed retroactively. I'd love to see you not whining at all if the government now turned around and said - as it could under the law - that unless you can show paperwork proving continuous residence in the UK since 1971 or whenever you started to work, you will get a reduced pension.
It's also an issue that has unfolded against a background of constantly changing legislation in respect of nationality and right of abode, which have been separated legally, and the fact that every single piece of legislation passed to clear it up seems to create new exceptional categories.
Bottom line, the people concerned came here legally and continued to reside here legally for many years during which there was no requirement to provide the paperwork you now reckon they should have collected. From approx 2010 onward, the government started demanding new paperwork and new levels of proof.
It's a bit like name change. There is NO requirement in UK law for things like a deed poll or stat dec. But over the past decade or so, the UK has drifted to a position where people believe this to be the case because of the practice of financial and other large organisations.
Where practice changes, a humane person might say it is not the responsibility of those adversely affected to have predicted the change.