Help with Vtg. Mid Century Modern Dining Chairs

[mikeamondo]

Hello all... newbies on the forum. Been buying / selling for years, but recently bought a truck so we could start playing a bit in furniture. I have indeed read the sticky post about not doing what I'm about to do.... if no answers available, then so be it... but if you don't ask questions, you can never learn something new!

Here are some Mid Century Modern style chairs, I believe do have some age to them. We've searched every combination of mid century modern + danish, czech, open back, etc. for hours (literally) and can't find any exact matched. No maker marks, but there is a number 375 95 stamped on the braces ... and shown in the pics.

Any help IDing them, and/or any info on suspected origin / age would be appreciated. One thing I was curious about... the braces are joined to the frame of the chair via groves machined in the wood to for a joint.... what's this joint called? Is is common or unusual, or does it offer any meaning at all?

Thanks in advance! Hope to become a regular in these parts!

Mike