The discussion at treasurenet.com has some well informed people on it. But one point it raises is not confirmed by anyone who seems to know. (The link comes from Why were US "Cavalry" belt buckle backs filled with lead?.)
That is that an expert on Pawn Stars apparently said the Confederate States never used a plain oval CS buckle (like the common plain oval US "cavalry belt buckle") during the Civil War.
Many established sutlers sell such plain oval CS buckles, and call them "exact reproductions." But so far none that I have found claim any source for such a buckle's original, unlike the US oval where they often say it is a reproduction of one found on this or that battlefield.
Can anyone find a clear confirmation or refutation of the Pawn Stars expert's claim?
Now I see Parsley's Brass has one found at Watt House Hill, Virginia, where there was (at least) a battle in 1862. The answer by @Steve Bird establishes, as he says, that such a buckle was not regulation in 1864 (or maybe just not used on sword belts but I'll go with not regulation). But I also understand that CS uniforms were a bit chaotic throughout the war. So I am not sure what to think.
Was it regulation at some other time? Conversely do other authorities besides on Pawn Stars say such buckles were not used?
The book cited by Steve Bird in a comment has at least one plain oval CS buckle on its cover (plus some ovals that may be box plates--but persuasive sources say the CS had no resources to waste on brass box plates). But I do not know if the book concludes they are genuine. I am trying to find the book on interlibrary loan but it is not going quickly.
Following that lead I found Fakes reproductions replicas with an extensive discussion of how many honest and dishonest ways non-genuine materials get on the market as genuine. It gives dozens of examples of non-genuine CS ovals but describes many of them as copies---as if there were genuine originals to copy. It is not clear about that.