Don't sign anything unless you know exactly what they are about
, and are sure you trust them. It doesn't matter that they are a big well known organisation - if they were really concerned about
you they would have contacted you two years ago and wouldn't be screwing up on the details. It is either some kind of legal CYA policy, or a dismally late attempt to research side effects (which they quite possibly don't want to hear about
really, because hearing about
them makes them legally "real").
By all means, write to them asking them to explain what the context of their request is, stripped of legalese. Ask specific questions to which they must answer yes or no (put on tick boxes, that would be fun for the lawyers !) It would be a shame not to have your experience recorded on a database, just in case it is pertinent; lots of valuable research gets done that way. But, watch out for small print...