I thought of that too but I couldn't try it when I had only Windows Search to test it against. Now, with exiftool, I can see the changes immediately but it makes no difference. There are two versions of the IPTC and that's it.
If I add new metadata and save, it will add to IPTC and if I then take it out and re-save it will subtract. But the IPTC2 info stays just as it is. That is data from a couple of months ago. If it would help, this old IPTC data was added using other software. "Other software" could have been Adobe, ACDSee Pro, or MediaDex. And a little bit XnView. Those would be the main ones I was using before I purchased Photo Mechanic.
When I got PM I went through everything trying to bring better order and consistency to my methods. The old metadata is not being recognized as 'irrelevant' by PM, obviously as it just keep hanging around in there and seems to be Windows Search's favored version of it.