I left a project in 2003. I can still hit their web login page, and I still see something specific in the URL I put there. I've no doubt they've upgraded some stuff behind the scenes, but they've likely not done huge overhaul, otherwise they'd have simply redone the auth process to whatever an upgraded system uses. They did change some graphics on the login page, and added a google tag thing, and converted some styles to css.

Very odd to look at it and know that I'm probably one of 2 or 3 people who know why that specific code is there, and also to know that the base of this is still running.

Remarkable. I also have some client side JS app of mine that's still alive and kicking on a very popular website 20 years after i've written it.

But that's the exception, not the rule.