I'm pretty sure the trial weapons are the versions only used during class selection. Actual games do that, where they name the test weapons that you can just try out as tutorial weapons, or in this case trial weapons, and then give them a similar or equivalent statted weapon that has a proper name on it, in this case low grade shoddy musket, when you choose it.
The idea is probably that it doesn't make sense to have an item called 'trial weapon' if it was a realistic universe, unless it was a prototype or smth.
Then why not call it 'low grade shoddy weapon' in the first place? Probably because the point is to choose between the different weapons and having a modifier with 'low grade shoddy' takes away from that.
Of course if they call it trial weapons later on, then this is all for moot.