If COPPA is not used in phpBB2, it is set in phpBB3 and vice-versa.
In phpBB2, if an address is entered in "COPPA Mailing Address," it is assumed that COPPA is to be used.
The phpBB2 convertor has
If no address is entered, is_empty returns TRUE, which sets COPPA in phpBB3 to be used.
If an address is entered, is_empty returns FALSE, which sets COPPA in phpBB3 to NOT be used.
What is needed is a function such as not_empty.