Company A finally wrote back to me in a letter dated 15 May, as per my previous posting.
Very briefly I will summarise:
They apologise for the delay.
They explain their decision process.
They note their key findings.
They reject my claim.
I will of course not let the matter drop; and will draft a detailed rebuttal of their points, over the next 10 days or so. This will be sent to the Ombudsman and posted on this site.