Every modern copy or backup program ignores it, and it looks like none ever used it.
In forums where people look for such things out of curiosity people mention they existed, but I've not yet found someone that owns one to play with.
And zero of them stopped the analog hole on those old devices.
Now, as to the actual bit(s). There were two bits, one said copyrighted work, one said is this a copy. Almost all CDs shipped with the copyright bit set and the "is a copy" bit set to 0. This meant you can make one copy of the CD (by law). The copy should have the "is a copy" bit set, meaning no more copies of the copied disc.
This means you can actually copy the original CD as many times as you want, since it always looked like an original, hence copyable.
Remember Sony hardware sold an order of magnitude more in value than Sony music :)
Again, a non-issue. To recap:
1. Very few CDs even bothered to set the bits. 2. None (?) set both bits, meaning you can copy any original CD, even with bit respecting hardware. 3. The bit(s) in no way changed the audio. 4. No copy software on PC I have ever heard of even looked at the bit. 5. Very few pieces of hardware respected the bit.
Did I miss anything?
CDs are pure audio data with error correction.