duck mount issue

Bugs or dermestids are a local issue and not the fault of the taxidermist.
It has been addressed several times here but if you have a bug infestation in your home they WILL get your mounts and NO mount is safe.
Most infestations start with "home taxidermy" items like turkey, grouse or pheasant tails or cut off deer skulls that still have skin on them. Other common avenues for infestations are bird seed, pet foods and even pets themselves. Dermestids, carpet beetles/moths are everywhere and there are LOTS of ways for them to get into your home but properly done taxidermy is not one of them.

Hire a good exterminator before you lose more mounts.

Surely bugs wouldn't pick on mount then quit. My living room has quite a few mounts. I would think bugs would move to other mounts also especially over two years.
Not to say it isn't bugs but I've had issues with this taxidrmist in the past and so I don't trust him.
I'll do a good inspection of all mounts today.

Bugs will eat whatever is most convenient first. Foot webbing is the easiest and quickest and usually shows damage first. Haired mounts like deer, foxes and coyotes usually take longer to start showing damage. A good indicator is finding what looks like fine sawdust under the mount or the larval "shells" on the floor and possibly in the hair itself. Two years is really not that long when it comes to a bug infestation. It often takes several years for a bug population to establish itself enough to do serious damage but thy WILL get everything unless you get them first. Like I said, look for sources of contamination like home taxidermy items, uncleaned deer skulls, turkey tails, etc or your pet food. They came in somewhere and it wasnt on a mount.

The other possibility is mice. Mice will eat the feet, toes and webbing of birds and then go away. Mouse droppings usually give them away.

Good luck in your eradication efforts.