We can all think of obvious difference between these three styles. Couture is the most expensive and hence has the most hand sewing and fine finishing, the most exquisite fabrics not to mention the most elaborate or unusual designs. But, theatrical costumes can be equally expensive with equally fine fabrics. But, they are made to withstand very hard wear and tear. While Couture put it's emphasis on perfect fit, beautiful interior finishing as well as exterior.
But, then there are differences you might not think about. The style of patterns used and even pattern paper is different between these 3 sewing styles. The way seams are finished as well as many other sewing techniques.
I plan to write a series of blogs talking about some of these things. They might not come out all in one week though. I am going to have to do some research and consulting to be sure I am getting it right.