1:1 to IRL match? No. For one, the UCM car was never tested in a wind tunnel (to my knowledge)
1:1 available data? Pretty much. Albeit the data given to me was basic (which is handy since I'm no physics guy) but yes it matches the rudimentary CFD data. And even "good" CFD data is known to be not that great.
But the point is, you should aim to match whatever data is available. For example, if you were making one of those lemans hypercars, the aero limits were published in the regs, so you should use them. You can be pretty damn sure the manufacturer teams like toyota will get pretty close to them. It is of course not a guarantee of accuracy, but its a lot better than nothing.
Its not about "every single necessary/unnecessary detail", its about getting it in the ballpark. And pretty sure that recently released LMH car is not even in the same postcode.