OP specified reencoding, which probably means converting lossy to lossy. Despite the fact that modern codecs (and even mp3, LAME is transparent at V2~192kbps for most tracks and everything except killer samples at V0~256kbps) are generally very transparent at low bitrates, the same guarantee does not apply when encoding lossy to lossy.

Think about it, if transparency guarantees applied for lossy transcodes, you could encode mp3 -> mp3 thousands for times with no generational loss. This clearly isn't possible.

Of course, you could rip all your files again in a better codec, but the time required to do that is pretty intense.

opus didn't exist when people were worried about 10 gb iPods