The instructions indicate that there are 15 generic cards for "Any Avatar" and 5 Avatar Specific, however my game with only 12 generic, 4 for each Avatar except the Beatman Overlord, who has 3. Is this correct?

I have 12 Generic cards (3 x Dark Strength, Siege Engines, Lawlessness, Big Trouble, Eldritch Lore, Enhanced Speed, Protective Magics, Transport Gem, Focused, Toughened.

4 Avatar specific ones for all the avatars except the Beastman lord who has 3.

This makes a total of 35, the front inventory of the RtL book claims 35 Avatar upgrade cards, The section under Avatar Upgrades on pg 24 does say 15 generic and 5 for each avatar as you mention though in my rulebook so I don't know what to say, probably an editing mistake on the part of Fantasy Flight, maybe originally there were 5 cards for each Avatar and they removed some, or maybe a reprint of the game is missing cards and more than one person was effected.

Add in the Lt cards and the numbers will match