Understanding Society User Support

Hi,
Can you clarify the key difference between the variable oprlg and the ff_oprlg variable in Wave 2 of the UKHLS? Are they pertaining to responses from different sub-sample participants?

I’m particularly following the BHPS participants through to 2015, and wish to know which religion variables pertain to them and which do not, but as far as I can tell, this is not easy to tell from the documentation. The frequencies of responses are very different for oprlg and ff_oprlg, which makes me think they are responses from different sub-samples, but which ones?

Thanks,
A