At least the website now gives you enough idea about the sort of information that you need to be collating.
The killer for many claims is going to be that the critical date will be date of purchase of ticket, not date of flight.
This will inevitably lead to quite a lot of disappointed people, who will equally inevitable rant without failing to understand the difference - and why the date of purchase was the logical date to use.
But one thing that you can do in advance is some research to identify all tickets purchased during the relevant period. My own experience was that it was harder to identify - although I think I've now got them all. And if you don't keep documents for this long, many of your claims may have to be based on guesswork.