I have seen here oft times of guys noting their guns fired with ZERO powder in the pan. I do not say it cannot happen, but have attempted to get it to happen
a number (lkike20) times and it never has, for me. That is, I pricked the vent after loading, to make sure no powder was poking in the flash channel, then made sure no powder granules were
any where around or in the pan, then 'dry fired' the lock 20 times, knapped the flint on about the 8th attempt, when I saw no sparks, then continues dry firing the lock to the 20th attempt.
It did not go off, and from this, I am not saying it could NEVER go off, just that it does not or has not happened for me as often as it was reported to happen - here.
An overly large vent hole would certainly assist in a non-primed gun going off.
I would suggest that is your lock had an exceptionally deep 1/2 cock notch, or a a dog-lock or 1/2 cock safety, that was applied after closing the frizzen, that the gun would be quite safe loading
if 1/2 cocked - indeed, loading at 1/2 cock with hammer closed was the method most often used, especially with self-priming pans.
I am still not suggesting we or anyone does this, just trying to address the reasons for the criticism of this method of loading.