Boeing was one of the first to deal with these issues (1962-1963). Read at least about the Boeing Model 853-21 Quiet Bird.
No, they were not.
The Quiet Bird was first publically discussed and shown on this very forum. The Quiet Bird - like most other stealth aircraft of that period - relied on RAM and a very limited amount of shaping. While that may have been state of the art in the 1960s, in the mid 1970s that all changed.
On or about 1975:
- It became possible to predict the RCS of complex shapes, which allowed the design of shapes with much, much lower RCS that previously possible.
- It became possible to build aircraft that would have previously been "unflyable"
- The XST program set a very aggressive RCS goal, and caused a change in how the aircraft were designed. Signature became more important than aero. Lockheed and Northrop designed very low signature shapes and then figured out how to make them fly. Previously it had been the other way around.
- The ability to accurately predict RCS also triggered changes in how radar cross section was measured (range design had been corrupting / inflating measurements and no one knew it until this point).
The Boeing guys did not know any of this until they started participating in the ATB program.