Some letters aren't letters

[ReneZ]

Your explanation doesn't account for the fact that it is rare in labels though. I'd be more inclined to explain it as an abbreviation or rather a symbol that stands for a common prefix or proclitic. If this is syntactic like Latin -que, the absence from labels is accounted for.

It was just a thought experiment and in its simple form it certainly cannot work.
The main point was that q (or even qo) cannot be a rendition of a normal character (letter) in a normal plain text.
It has to be 'something else'.

One has to be really careful with abbreviations. Expanding abbreviations lowers the entropy.
Going from 'Voynichese' to 'plain text' one almost certainly needs to increase the entropy, so this process should ideally not include expanding abbreviations.
The word final y (topic of a future post) may have been inspired by the Latin abbreviation for -us, but we can be certain that it does not mean this in Voynichese.