I am not an expert on poch but like Poncho I am a variant collector and have an interest in PBP / Poch.
First of all there is a big difference between PBP and Poch. You are correct when you say PBP were common as they are often found in the UK as the PBP figure was commonly found on Palitoy cards.
There are at least 3 known capes that come with it:
- smooth cape
- rough and Matt cape
- rough and shiny cape
I have a small collection of PBP Vader's and all 3 capes that are found in Javi's Made In Spain book.
The PBP Vader though is found with the scarred or blobbed out coo and does not have an epm in the back.
The poch Vader on the other hand is found with two Hong Kong coos, neither of which look to match your coo Mulbin. As you mention the paint app on the chest is different. In addition one of the Kenner factories made a Vader with the epm on the head and while not as common still easily found, as is the degradation / bubbles on the head.
I also have a Kenner Vader (Pics attached) with the correct coo for a Poch with epm and bubbles on head but when I had a conversation with Javi he was confident mine was not a Poch. As well as the coo, it is often found with the scar like Ponchos, a small residual burr between the legs, melt marks and different paint apps.
So although not sure I don't think yours is Poch Mulbin. I'd be interested to see yours naked Poncho.
Jay