Valbazen is a Benzimidazole. Benzimidazole's are mostly excreted when given to poultry, only a small amount is absorbed into the bloodstream. There will be minute residue in eggs.
We eat the eggs after worming birds with Valbazen or Safeguard. I'm still here typing.
However, if you suspect that you or a family member might have a reaction to albendazole, by all means discard the eggs in the garbage for 2 weeks after the last dosing. Do not sell nor give away the eggs to be eaten.
You can gather fresh fecal samples in a ziplock bag and take them to your local vet and have the vet look at the feces under a microscope for worm eggs. If none are seen on the slide, no need to worm your birds.
Odds are you'll never see evidence of worms in feces. Worms are parasites, why would a parasite want to leave its host?
The only time you'll see worms in feces is if there is an intestinal overload, or a worm has died of old age.
Keep in mind that one female roundworm lays thousands of eggs onto the soil. Chickens constantly peck the soil and pick up worm eggs and swallow them, infecting the chickens. If you get the chance, take a look at the poultry roundworm lifecycle.
Your soil dictates how often you should worm your birds.