well, high frequencies are curtailed on all but the very highest settings, and channels are mono-ed at high frequencies where stereo positioning information is lost on medium settings. Compression depends on masking, ie foreground sounds are encoded and background sounds are ignored. So mp3 compression is not like zip which can be restored to its original state, it throws away information which can never be restored.
The amount of compression threshold of differentiation will differ between people, source material and playback equipment like any other subjective judgement.
Making your audio cd from a mp3 of your wave recording does not restore the original wave quality, just effectively re-records your low bandwidth recording at a higher bandwidth again needed to make an audio cd. An analogy might be taking your 15 ips half inch 2 track Dolby A reel to reel recording, recording it on a good quality cassette with Dolby B, and then recording the cassette output on high speed reel to reel with Dolby A again.