Please add one more picture of the mark you described on the back.
Refrain from rating this question until I have had the chance to see the back stamp and answer fully about your plates.
The mark in blue is a fake Sevres mark. This mark is the decorator's mark only (the studio that painted the plates) and represents Paris Porcelain from 1890-1920. The actual maker's mark is underneath the gold crown that you mentioned. A single razor blade will scrape off enough of the crown to reveal the actual maker under the crown. Sometimes you can hold a plate to strong light and read the mark without scratching off.
Please do not respond to the automated email asking you to prematurely rate me.
I am right, I see this all of the time. The maker was covered to avoid tariff and to make it look like the decorator also manufactured the piece. Sevres had no B in the middle of their marks and this is a known faux mark, not necessarily a bad thing and is considered common.