If it comes to light or an appointed brother confesses that he has committed a disfellowshipping offense years in the past:
The body of elders may determine he can continue to serve if the following is true: The immorality or other serious wrongdoing occurred more than a few years ago [subsequent BOE letter specifies minimum of 3 years], and he is genuinely repentant, recognizing that he should have come forward immediately when he sinned. (Perhaps he has even confessed to his sin, seeking help with his guilty conscience.) He has been serving faithfully for many years, has evidence of God’s blessing, and has the respect of the congregation.
has evidence of God’s blessing - Has said elder been putting out for the Borg?