"...as far as I know trousers have never been issued to German regiments."
Well, clearly, whether for drill only or not, they were issued (at least for the Nr. 3 Erzherzog Carl Regiment). The evidence is there. Of course, you are free to ignore it.
Have a nice day.
Opinion, you are right in asserting that in matters of uniformity things are never static and that we must not have too rigid a vision of the soldiers' appearance. Do not misunderstand my writings: there is a big difference between saying, the pants were not worn by the grenadiers, never and everywhere and say that it probably happened, but in a marginal way so that it does not appear in a systematic way in a production of figurines. As far as I am concerned this is the last option I chose. I appreciate your intervention which allows to qualify things.