Yep that is what I meant as well as the fact that all the best girls are not event girls (bar a few) so you are not likely to have 4 slots open on many and thus you should already have many defence earrings that are not being used.

I have 14 event earrings and only 1 is being used because only 2 of my girls have 4 slots open and the other has enough defence with the bracelet and necklace.