Welcome aboard General!
I can understand your desire for your Girl not to know about that part of your past. However, the incident has brought it into view, so it will have to be dealt with. The good news should that all you may have to do at this time is to tell her that you were raised in a cult (that is what it sounds like from the story), and left it years ago. You can probably say that the two assholes were local leaders of that cult who knew you and too stupid to realise that 5 years of not being there constituted a severance from the cult, so, they assumed they had some sort of authority over you. Tell her that beyond that, you are not really all that comfortable discussing that part of your life since growing-up in a high-control cult is not a very nice exprience. hopefully, she get the hint and be satisfied that you thought enough of her to reveal that much.
If you marry her, you'll have to eventually tell her more, but if she loves you, she'll let you do it at your own pace (I hope I've got it right Ladies, if not, feel free to be frank with us guys since our new friend needs good information to base his decisions on).
If the elders invite you to a JC, then they are not following the directions of the mother organization. They've seen enough to conclude that you've Da'd yourself from the organization and have no further need to speak with you. so more than likely you will hear from your mother that she cannot speak to you since you've been announced. If nothing along those lines happens, then you might want to be prepared to get a little more specific with your GF if you marry so that she won't be blind-sided by your mother's conduct. If it does happen, you may have to be prepared to tell her enough that she won't be blind-sided by the attitude of oyur JW relatives anyway.
That's the whole thing as I see it. Keep us posted General, for all our squabbling with each other in some of the threads, we are here for those are walking the same paths we are.
Forscher