I found BL_AGE after FU_END_AGE in the endpoint data, how is it possible?

This can happen when an individual gives biobank sample after register follow-up ends. For example, if FU_END_DATE is 11.10.2021 (DF9), and individual gives sample to biobank in year 2022, then the BL_AGE is currently after FU_END_AGE.

Other case when this can happen is if an individual has moved abroad (in this case FU_END_AGE is age at emigration), but moved back later and gave a sample to biobank. In this case BL_AGE is after the FU_END_AGE and difference can be several years.

Take a look also at the section Complete follow-up time of the FinnGen registries – primary endpoint data