I think the approach taken by Cross Country XC) - who delivered SWTSMBO and myself to Wakefield an hour late on 24th December (although the fault actually lay with Network Rail, Mother Nature or god depending on your view of these things) - might be best in that you submit an initial basic claim and then get a pretty rapid holding reply which invites the submission of relevant additional information, something which can be ignored for simple cases.
However I was a tad surprised that XC insisted on having the name and address of my fellow passenger so that they could pay two separate refunds if it was deemed appropriate. Presumably somebody in XC customer service has misinterpreted the meaning of 'Delay Repay'.