Yeah, I actually once worked at a place that was clean-rooming. They went to absurd lengths, even WITHOUT the old source code.
If you were designing the new app you couldn't even -look- at the existing UI; you could only get descriptions. Every term was checked by legal to make sure that it was a 'standard' industry term vs something that was specific to the existing software. They even used a different tech stack wherever they could.
I think the other company still tried to sue, IDK how it played out (I was gone by then) but I remember at least thinking they were in a pretty safe spot with how they handled it.
If you were designing the new app you couldn't even -look- at the existing UI; you could only get descriptions. Every term was checked by legal to make sure that it was a 'standard' industry term vs something that was specific to the existing software. They even used a different tech stack wherever they could.
I think the other company still tried to sue, IDK how it played out (I was gone by then) but I remember at least thinking they were in a pretty safe spot with how they handled it.