Earlier quoted context omitted.
this is specifically the reason minidisc is built around a lossy compression codec so there would be at least some generational loss from copying. Sony themselves were/are a label and this led to deliberate worsening of their electronics at times.
Were disc->disc transfers not digital? I would expect to not have to decode/encode (and thus suffer loss, if the encoder weren't deterministic) if you're transferring disc to disc.
There was one way around this: the MDS-W1 (http://minidisc.org/part_Sony_MDS-W1.html) could move tracks in raw data format between discs. Of course, it erased the source track, but if you did this twice (it defragmented as it went) and then TOC-cloned, you could have two identical MD's. They're available on eBay, but they're $400-500 and ship from Japan, so good luck powering one if you're in Europe.
It really was a lovely format that was crippled by the music side of the company. 170 MB on a rugged, infinitely-rewritable, non-accidentally-erasable format that was smaller than a 3.5" floppy?