Gen1 stores the pkm's catch rate when it is captured and is unused. Transferring to gen2 converts it to an item if necessary. If you remove the item, the value is 0.
You can't trade Gen1->Gen2->Gen1->Gen2 to constantly make items.
Probably was edited/modified prior. Loading a gen1 save with tradebacks disallowed shows your Pigeot as invalid (as the catch rate data needs to be valid, which isn't, because the held item was removed at some point).