I found this image of Queen Victoria, and wondered if it might depict the basic tiara but without the addition of the sarpech elements seen in the tiara worn by the Duchess of Connaught?

There are several things undermining this idea: the sarpech element may be an intrinsic part of the design and construction of the tiara worn by the Duchess. I cannot tell. Secondly, the artist may not have done this miniature from a life sitting and it may be a complete figment of his imagination.

RCIN 19525. Said by the Royal Collection to be circa 1837-38.