Probably 80% of pinholing issues are related to the bisque firing, not the glaze firing.
Most of those deal with a lack of sufficient oxygen able to circulate through the densly packed wares to allow some body reactions to go to completion.
Secondarlly, thermal lag in a tightly packed bisque can mean that a lot of the wares are not fired to the witness cone level )or the sitter cone level or the computerized controllers idea of what the kiln did).... but to some level of heat work below that. So there are reactions that are not happening in the bisque that should.
Does this problem happen on certain types of forms more than others? Bottoms of bowls that have been heavily "nested" in bisques is a typical indicator of this issue. Ditto for anything that is contained "within" other forms. And also for stuff toward the middle of the stacking of wares... the furthest away from the electric elements.
Changes to the bisque firing profile or stacking techniques (slower firing, better air circulation, less nesting and density) or slowing down the front end of the glaze firing can alleviate this......assuming that you are not using glazes on the wares that have a very low start to the sintering/melting process... and thereby make the surface gas impermeable before oxygen transfer and the outgassing can take place.
PS: I fettle often. I use a lot of natural matreials glazes.
Professor of Ceramics; New Hampshire Insitute of Art
Guest Professor, Wuxi Institute of Arts and Science, Yixing, China
Former President and Past President; Potters Council