First of all, there is no blood test that is accurate for PDD/ABV. Find out what lab the blood was sent to. There is an Ohio lab that constantly has false positive results. One of the only accurate tests is collecting feces for 3 weeks and freezing. The Texas A&M then mixes all together and tests. PDD/ABV are not always actively shedding, that is why 3 weeks is needed.
Furthermore, plucking has nothing to do with PDD what so ever. It usually presents with undigested seed in the feces, vomiting and neurological symptoms.
Where are you located? What vet do you use? and what lab was the blood sent to? If you wish you may PM the answers. Please do not waste your money having the other birds tested yet till you get the conure tested correctly.