You need certified logbook evidence for each launch endorsement (winch/car, aerotow, bungee & self-launch) you want to include on an EASA sailplane licence during the conversion.
You will be asking somebody to put their name to a legal document attesting to the bona fides of some bloke they only met 5 minutes ago, on the basis of a few dog-eared 10 year old documents. They're unlikely to have launch records from 10 years ago so it would probably help if there are people who remember you. I'm sure the BGA & clubs would like to be helpful but a helicopter instructor was recently sent to prison for being too helpful.
OC619, your best guess is the definitive answer. I recommend the comversion guide from
this BGA web page.