There is no "forgetting" that causes a leak.
If a joint was missed, then a semi-qualified tech would have noticed it BEFORE they put refrigerant in it, and BEFORE they hooked a vacuum pump up to it.
After all connections are made, nitrogen is put in the system for the purpose of leak checking. This would have shown the leak.
After the system appears to be leak free, a vacuum pump is use to pull the system into an extreme vacuum. This would have shown any leak that the nitrogen did not show.
The fact that someone "forgot" to braze something means that they didn't use nitrogen for leak checking.
It also means they didn't use a micron gauge. (this measures how good of a vacuum is pulled, and also shows if the system is "dirty", or clean.)
Or, they didn't do any of the above, in this case, you need to upgrade from pissed to extremely pissed.
Back to the original post.
After 6 days, I find it hard to believe that the refrigerant is still in the attic.
If refrigerant was so easily contained, that a attic would hold the refrigerant, than the entire idea of recovering refrigerant is out the window.