OK, there are couple of tables that have special characteristics too.
PartCost can have multiple records per part. Find the CostID for your Plant (ours is ‘1’). The link will then look like:
VendPart has Effectivity Logic. So, there can be (and probably are) more than one per part. This will definitely give you duplicates. Add the EffectiveDate to your display and you’ll see what I mean.