I created a mosaic dataset with overviews for 2012 tif images and 2015 tif images that cover same area, are indexed the same way. The mosaics are in different file gdb. When I add either mosaic by themselves into an mxd all levels display correctly. But when I add both of them one will not display any overview levels. Zooming in will display the actual image.
2012 had pyramids built before mosaic was created. 2015 does not have pyramids.
I ran Calculate Item Visibility on both, also tried increasing Maximum Number of Rasters per Mosaic. Didnt help.