I can think of 3 in the last few years, UNI twice and NDSU once.
Few years may not be accurate, I remember UNI beat ISU in 2013. I cant remember how recent the other Panther victory was.
Add that to Toledo this year and Tulsa in the bowl game, 2012?, and you have at least 5 losses to non power 5 teams in the last 7-8 years.
I would have no idea the total going back 17 years.
Since 1999 you are right on Iowa's losses. They lost to 0 FCS schools and 4 Mid Majors as you cited.
Iowa is 19-4 vs Mid Majors since '99 and they are 10-0 vs FCS schools.
This is interesting, I would have thought that Iowa would have played more FCS and MidM schools as they played less conference games, but ISU has played 40 games vs FCS and MidM to Iowa's 33. I did notice that most years Iowa played another Power 5 school, whereas we always played pretty much Iowa and 2 Mac/FCS schools.
If ISU would just win those easy games at the same rate Iowa does, we would have an additional 3 wins vs FCS schools, and be 21-4 vs MidM. That would give us a total of 8 more wins. This is what is so tough to swallow, we just need to beat the easy teams, and things would be so much better.