Consider a large enterprise having 300 developers in multiple teams, I am not at all surprised that they can manage to write 100 million lines or so. Also I think this is really a system of systems, and in my experience probably has large parts developed by the lowest bidding firms. Which when software is developed for 10 years or more means more than one way to do the same thing.

Also having to deal with lots off ancient systems and working around weird bugs probably fixed years ago. You know things like bugs in Java 1.2 on HP-UX and stuff like that, or errors in Oracle 7i etc...

Plus functional duplication because team A did not know subteam C2 build the same thing...

Editing my comment instead of replying to the excellent comment by @jacquesm as hn does not allow me to reply to the reply.

Actually completing the transfer of a codebase like that is unlikely to a new team without much much more of a handover. But some high/middle frustrated with the current system manager asking a team to start rebuilding before it gets shut down a few months/years later is very possible. An other plausible option is a corporate take over... But then I would expect a very experienced team to work on it who do not need to ask HN for this kind of thing.

I personally have been in a situation where code moved between companies and no documentation or old developers where available. Not as large as this only a 1 or 2 million lines of code/xml. But I am no longer surprised by the stupid acts that large corporations can perform.

And this must be systems not just one. You can't build a single jar file of 50+ millions of lines of code than could have loaded in a JVM around 1.3.1 on even high end hardware for the time.