Ah that could fitwith what I just posted... that they don't keep the dogs in till they start reacting to whatever was in the shed and I guess they might not to do that immediately as the scent would build up the longer it was kept there . And even then they might think it's drugs the dogs can smell rather than a body, especially if there was no obvious smell to them.
Only dogs that are trained to find drugs would be interested in the bags of drugs. There's no way the bags had no smell, plastic doesn't block the odor. Now if I had packages worth a lot of money the last place I'd leave them would be outside in a shed, I think they knew to keep them out of the house because the smell would drive them out of the house. I had a freezer that was put on a bad circuit I had meat in professional sealed packages and it stunk so bad I couldn't stand it. The freezer had only been off for a week so it doesn't take long.