David inherited a codebase that's a few decades old. As each developer has taken it over, they've done their best to follow the code standards that the previous developers used, to at least keep the codebase consistent. A few rebels may have gone a different route, like the right one, but too many just followed the patterns that were already there.

This means that there are a lot of variables named things like a and aa and aaa. There are 4,000 line functions and loads of copy/pasted code.

In other words, all the usual markers of bad code are there. But the special feature that David inherited is that in the code, this is a common way to express an if/then/else:

if (someCondition)
{
	DoTheThings();
	goto skipIt;
}
DoTheElseThings();
skipIt:
//program continues

Not every conditional is written this way. There are a few developers who, as they modified the code, tried to whip it up into some sort of sane shape. But not enough did that. So these kinds of blocks are just scattered everywhere.