Hello Indigo Sunset,
I'm not sure whether my experience will help: I happen to know that when Balenciaga in the UK send their sales stock to the Bicester Store, they will print new tags as the old ones are no longer with the bags. This often results in Dates/Seasons not being accurate.
I know this as I was there only a few months back and spoke to my favourite SA there ( I also know the SM as well who used to work for Balenciaga in London). This is common practice and the tags should therefore not be taken as gospel.
So if the reason your bag had reg flags in the authenticity thread then it may be to do with this. The bag (Twiggy) looks suspiciously like the ones I saw back in May in Bicester. And I can assure you that all stock at Bicester is authentic Balenciaga.
I hope that gives you some reassurance. Let me know if I can be of any more help.