An interesting fact about MP3 compression, is that the actual encoding procedure is not constant, but that the decoding procedure is. This means that many of the differences that have come to MP3 in recent years, are optimizations of the encoding, which when played back in an unchanging way, may give better results.
For example, I myself have often written, that to quantize the frequency coefficients is ‘good’, but that to cut them off because deemed inaudible is ‘bad’. Well, why not just set all the assumed audibility thresholds lower? It would not affect the actual decoding of the stream.