Convents and holy sites are much more likely to remain undisturbed. In many other western european sites, every other inch of land has been farmed continuously for centuries, making it unlikely to find an undisturbed body. This wealthy woman was in a lead coffin at a convent, and was probably much better protected from the elements than 99.99% of her contemporaries.
I didn't claim a miraculous explanation; I only said I no longer think these cases are faked. I think "incorruptibles" are a fascinating phenomenon that I can't explain. I believe in miracles, and I think some incorruptibles might be miracles, but I don't really know. There might be other ways that the lifestyle we tend to call "holy" does something to retard decomposition.
However, I don't think your explanation is sufficient because decay usually begins immediately upon death due to the presence of organisms already in the body before death. Sealing the coffin would not prevent such decomposition.
Convents and holy sites are much more likely to remain undisturbed. In many other western european sites, every other inch of land has been farmed continuously for centuries, making it unlikely to find an undisturbed body. This wealthy woman was in a lead coffin at a convent, and was probably much better protected from the elements than 99.99% of her contemporaries.