We know that some of the descriptions attached to items in the online collection of the Royal Collection are not entirely reliable. I could name one that says Queen Mary is seen wearing Queen Victoria's State Crown (when it is clearly Queen Mary's personal crown). I have already contacted them about that error.
It does seem to me that the QV State Crown, small diamond crown, and Regal Circlet have become muddled in various sources. Just how far back that might extend we can only guess. (Shall now look at a few more books.)