It is my understanding that Forstman was the wool weaver - they manufactured the fabric that was used. Most suits I have seen just have their label, but I have seen some where the designer label was present, and placed just above the Forstman label, in the side placket. I would need to seriously check my archives, to find where this information came from. And, I can look into my sold archives to see if I have an example... very high quality, that's for sure. And you and your mustard suit are utter perfection!
Editing to add - I searched my sold archives and found a 50s suit by Rafi that also had the Forstman label and a label for Olds and King, the department store it was sold in. I knew I researched that for a reason. I was trying to find a suit that sold to SNL, but I'm either not recognizing it or the search isn't turning up Forstman, anyway.