the most important piece of software to be built/maintained (ie, typed) with Notepad++ is of course Notepad++.

And I’m not sure this is even true. :-)
At least when I’m doing development with Notepad++ source code, I use the Visual Studio editor/IDE, not Notepad++.
Not sure what others do (but I would suspect the same).

Notepad++ is a text editor, used to type anything you want to type. Trying to enumerate everything ever typed with Notepad++, or even list every major company who ever had an employee use Notepad++ to type at least one line of source code, would be a pointless exercise that could never have any meaningful outcome. I don’t know of any text editor whose website brags about places that used their texteditor to type code. And of course, the most important piece of software to be built/maintained (ie, typed) with Notepad++ is of course Notepad++.