Hi
It is interesting to know why, among others, it contains a clause stating that excess substances cannot be drained back to the original reagents? what could be dangerous about it
I think it can be two things. 1. The vial, in which the reagent was transferred, can be dirty. This way by putting the excess amount back to the main container you can spoil the entire amount of the substance, and it is two much of a risk. 2. The compound can react with atmosphere, so this way you'll just add slightly decomposes compound to the rest of it
And if you take into account the work with clean dishes and stable substances, this is unnecessary
You can also just mix jars or something. The main idea is it's better to sacrifice a small part of the compound raver then have a possibility of ruining entire batch
Again, here it is worth starting from limited substances already, i think