Bibs are filled by gravity, and for the most modern machines, after being filled by a neutral gaz, usually nitrogen,sometimes argon, but certainly not under vaccuum.
Though I don't have any precise data, filling bibs exposes the wine to much more air than filling bottles, mostly due to filling speed.
Therefore I have to use more sulfur for bibs than for bottles : 30ppm to 40ppm for 5 liters Bib, against oxydation only. Which means around 45 to 60 ppm addition at bottling (to be compared with 20 to 30 ppm for bottles). If the wine is not filtered nor fined, at these levels of free at bottling, the remaining free SO2 will be around 0 after 2-4 monthes. And we all know what 0 free means in terms of stability on early "bottled" wines. I guess a bib of Allemand sans souffre would be much more stable than my Ctes du Rhne...
Probably as stable as a lot of so called sans souffre wines... I bet it won't be long before we will ear of a "indigenous sulfur" concept which could explain the actual level of sulfur one can measure on the vast majority of these wines.
So according to my experience, unless one goes for totally sterile filtration and bottling or a very reliable cold chain, an addition under 40 ppm of SO2 will lead to oxidized and (or) unstable wine within a few weeks after conditioning.
Plus, the bags are very porous to CO2. So the classic trick of the real sans souffre, bottling over 1000ppm of CO2 won't work for long.
Real 0 sulfur freaks stay away from bibs!!!