Ahh. Right. Yes, sometimes a longer explanation would save much confusion - particularly when I am juggling so many streams of development...
In direct answer to this, I already abandoned the idea of extracting ASIN - as there are two few books that have this to justify the effort (particular given there is no pattern to the number itself). I will leave it up to the Amazon plugin in Calibre 0.8 to populate it.
The new Extract ISBN is ready for release now, much nicer with it running in the background. I will release it when 0.7.58 comes out as mentioned above, anyone running from source is welcome to PM me their email to test it.