Murrle Bennett (?) Necklaces

I've read there's a difference between the circled stamp of Murrle Bennet vs. the plain 950MB, suggested to be from the earlier works. I'm wondering if anyone has an idea about these two? They both have the plain stamp, but I haven't seen the same necklace with enamel work, most have a gem included. Could they be a reproduction?

A total mystery to me! Found them in a second hand store :)