If I remember correctly, it was said in another thread that Tegleva testified that the jewels were sewn into "kostyumi" which is a different word from the word used for corset which is "korsyet". It is also true, as pointed out above, that the remains of six corsets were found by Sokolov at the mineshaft, thus accounting for all six females. Interesting to look at the photograph of the front busks of the corsets found, which clearly shows the difference in length of the front busks.
Also as anyone who have worn a proper corset can testify, there isn't place to stuff a tiny baby mouse in between a corset and your body as it is custom made. They would have been blue and bruised, not to even mention the pain and discomfort. If the corsets were involved in hiding jewles at all, it would have been sown onto the outside of the corsets and then covered in wadding and material sewn over that onto the corset itself to disguise it.