I avoid multiple NA lists
I had the same problem. This is what works for me: I keep a single NA list per context. So even if an email is actionable, I decide the action, and put it on my NA list. I do keep the email in my @ACT folder, but only so that I can find it quickly. Reminding of the NA is not the purpose of my @ACT folder; that's the job of NA list. In fact if the original email is not required for the action, I do not move it to @ACT; I archive it elsewhere.
This also has a further advantage that I don't have to figure out the action associated with the email again at the time of acting; that has been clearly done when I decide the NA.
Maintaining a satellite email gtd system has never worked for me. I do not even have a @Waiting kind of email folder; I maintain those with other @Waiting items in the master inventory.
Hope it helps,
Simple fix to close the loop
You mention a pda, so I assume you sync it with one of your computers (work?) and somehow get email NAs from that computer into the pda?
If so, the simple fix is to forward those emails from gmail that have or are NAs to the email account you generate your NAs from