Looks like another Dithering step is inevitable, as I am indeed using a safety limiter (which in turn can result in new harmonics) and fade in/out (on the fly via the montage). The client provided material that was “limited to -0,1dBFS” - but it results in overs (up to +1dB), and of course no proper fade in/out.
So MBIT+ it is.
Thanks for the answer - really helpful.
Might be something for a manual update as “things to look out for”.