This sounds so much like dealing with MS Access databases... Unfortunately, part of my responsibility in my current role is to manage a handful of Access applications... they are ancient, I am talking early 2000's. They are the most unruly thing I have ever had to work with, and I will not go into details but your story reminds me so much of having to work on these apps...
MSAccess is a tragedy, imo. Right-up until, say, Access 2007, it was a simple (in a good way!) RAD platform following those zombie 4GL predecessors, but it’s been left to stagnate without any real effort to modernise it, and it’s clear from how Microsoft’s been downplaying Access that it’s a product they’d really rather not have to support, but they know if they do kill it then it would weaken on-prem Office’s moat and everyone will probably just rush to Google Firebase.
Most of Access’ problem is how it’s inseparable from both VBA and COM. While Microsoft has tried to make COM sexy again with WinRT and C++/CX, VBA is quite senile now. Microsoft has killed VBA in Outlook, killed VBScript in Windows Server, and is now trying to kill VBA in Excel too. MS is pitching modern JS as a successor (which I’m not too mad about…) but I just don’t see how JS could unseat the sheer volume of Access VBA out there. Especially as “Office JS” is intentionally kneecapped for things like local computer files and Win32 so it has feature parity on web vs mobile app vs desktop - it’s going to be awful.
