This little saga goes on and may have come to a logical conclusion. From the original 8 flights, x3 were cancelled by VA and refunded to the travel bank (see above), x2 I moved to a later date as these would have been cancelled and I did not want to restart the process of chargebacks and dealing with AMEX. That leaves x3 cancelled flights for which conditional credits were issued.
As a further update I have received copies of the information that VA provided to AMEX and after seeing what was provided I requested the cases to be reopened. As for conditional credits - VA are telling AMEX a conditional credit has been issued and that is the end of it, they do not go into detail what this means. VA were also happy to provide VA with an extract from their conditions of carriage highlighting section 12.5 and underlining "events beyond reasonable control." VA also requested that AMEX close the charge backs
After reopening the cases I provided AMEX a copy of the judgement for conditional credits and how they could be used, I also provided another copy of the Guest Compensation policy which details refunds will be given and was published at the time the booking was made. In my email to AMEX I requested a refund for the x3 fights that had been cancelled and conditional credits applied. I have noticed that AMEX have refunded 3 flights and hopefully this time they will stick.