These PNRs are stored on mainframes running software written in COBOL which has not been touched for years. The actual PNR is a flat text document with semi-structured lines as explained in the article.

We never make changes to the mainframes, we just wrap the functionality. The structure of a line cannot change as the industry relies on all airlines using the same structure. If a new "field" needs to be added to the PNR we add it as an "RM" (remark) entry.