Rear wheel bearings failed

[CountrySquire55]

Installed new cast iron drums all around about 2500 miles (2 years) ago. Rear bearings were brand new along with the grease seals and lock rings and fully greased with high temp wheel bearing grease when installed. During a long road trip about 800 miles ago, left rear brake locked up after getting super hot. Readjusted the brakes and continued driving. Kept greasing the rear bearings (so I thought) through the grease fitting on the back side of the backing plate. Yesterday, removed left rear drum to inspect due to strange noise and found the bearing totally lacking grease and completely disintegrated (parts fell out of the drum as I removed it). The race looks OK, not scored. Removed the right rear drum and found no grease and the bearing about ready to fall apart. It appears that my efforts to keep the rear wheel bearings greased through the grease fitting were not working and not sure why. I have removed the grease fitting and tried to work a piece of safety wire through the passage but after about 1.5 inches, I cannot move it any further. Both rear hubs look like they have had new races pressed on. I want to make sure my new bearings stay greased so this problem does not happen again. Is there some grease passage way in the hub that could be blocked? Should there be some kind of hole in the hub (that is now covered by the pressed on races) to permit grease to get to the bearing from the grease fitting? I am not sure what to do next. Any suggestions? Thanks for any advice!