Is the AgeAtFirstClaim variable in Members.csv the age of the member in Y1, or their age in the year of their first claim?
In other words, say you had two members, both with AgeAtFirstClaim = 20-29
The first member has claims in Y1,Y2,Y3, so they are presumably aged 23-32 in Y4
The second member only has Y3 claims. In Y4 are they aged 23-32 or 21-30?