Your use of the bag in bag WILL NOT ACHIEVE THE DESIRED OUTCOME.
According to my understanding of intercept bags, they MUST BE CLOSED/SEALED in order to be effective. They NEUTRALIZE harmful gasses enclosed WITHIN the seal and PREVENT harmful gasses outside of the bag from ENTERING.
If you have left the Intercept shield bags OPEN, then you have rendered BOTH Intercept benefits INEFFECTIVE.
As Chris will likely explain, the vaccuum seal bag does not perform either function of the Intercept bag and serves NO PURPOSE for coin preservation.
I have to stress that what I have described is not how the manufacturer of the Intercept bags has recommended for the bags to be used. Therefore failure of the "experiment" to produce results that are similar to those claimed for the ideal use of Intercept bags cannot in this instance be blamed on the said Intercept bags.
Vacuum sealing of the whole assembly as I described above has the net effect of removing most of the air between the bags and the coin slabs and between individual bag/slab components and the food safe bag. At the end of the air withdrawal process the two leaves of the Intercept bags above each slab are closely and tightly apposed to each other to the point of providing a virtual seal of each bag.
But that is not the main closure mechanism in my set up; heat sealing of the food safe bag provides an additional barrier to air entry into the vacuumed space. I do not have any data regarding the coefficient of diffusion of air and toxins across the plastic material of the Intercept bag compared to that of the food safe bag. I don’t know which is a better barrier. But virtually all plastic sheets are somewhat permeable to the diffusion of gases.
Equally important to me is that vacuum sealing these bags and slabs like I have done protects them from ambient water vapor in addition to accidental water immersion. Furthermore, a plastic bag with a sealing clasp may be waterproof (or water retardant) but cannot guarantee 100% exclusion of water from the contents in cases of total water immersion compared to the vacuum sealed food safe bag set up I described.