assuming this
https://www.caa.co.uk/WorkArea/Downl...?id=4294976461 is the CAA flowchart you have seen,
then note 4 seems to imply that initial Class 1 applicants who have been free of migraine for 5 years (though it does say 10 years in note 5) can get an unrestricted class 1 with a favourable Neurologist's report, (and I don't think an initial certificate can be issued with an OML any more anyway). Since you are now more than 10 years that sounds vaguely hopeful.
I also interpret the flowchart to mean that a history of Migraine requires a CAA decision on initial issue (that's what refer to AMS means in the top left hand corner) so even if the Aeromedical Centre you attend for an initial Class 1 feels all is OK, The CAA itself will make the final decision.
These flowcharts may change so these comments only apply to the flowchart as it is today!