[JdeBP]

... and one that is only a few months before ISO Recommendation R 2014-1971 formalized such things. The "everything old" idea applies to ISO 8601 too. I myself was using these date formats, complete with the century number, several years before ISO 8601:1988. I had to touch nothing of what I had written to deal with the Century Bug.

Ten years after the turn of the century, I was still dealing with the interoperation between my approach and softwares that used 2-digit years: http://catless.ncl.ac.uk/Risks/25.94.html#subj11