Read a few convincing sources and apparently 'c' wings could be converted to 'e' and that is the likely explanation for supposed '1943' MkIX e wing aircraft.
The first production run (brand new) MkIXe were delivered in February 44 and that batch was completed in April 1944. At the same time instructions to convert 'c' wings to 'e' were sent out.
main source:
http://spitfiresite.com/2010/04/sort...-mk-ixxvi.html
Unit 353
Should have available date moved back to Feb 1944
Thanks Michal
Cross