Topband: Binocular Cores

[Roger Parsons via Topband]

I have some binocular cores which I know are FairRite mix 73. I have others which I thought were also mix 73. However, the first ones measure about 50k Ohms with ohmeter prods onto their surface, whereas the others only measure about 1k Ohm. I don't believe that that is a defined parameter, and am aware that the test is not very scientific, but I am surprised to see such a difference. Thoughts?
73 RogerVE3ZI