That would take, as academics say, a good deal of research. But I would imagine two things: (1), it would be unlikely that reports now are more inaccurate. The reason I say that is that it is much, much easier to check. In the course of my time in journalism, checking has gone from a rather laborious finding a book, finding a reference book, which may or may not be in the newspaper, library, or going somewhere to check -- say Companies House to check companies' records, which meant, of course, an expenditure of time and therefore one wrote less.
Now all kinds of tools are available at the touch of a mouse. So it is much easier to check and I think -- I would imagine that my colleagues in all newspapers, assuming that they do check -- and I think most of them do -- probably get things more right than they used to.