First up, here's a charming blend of two episodes from 'Dragnet' which basically tell the same story, but in different eras of the show:
The repetition of a plotline isn't uncommon in Toobworld, but not so often within the same series as the original. It became a standard in 'Bewitched' once Samantha altered the facial appearance of her husband Darrin; and it was the first sign that homicide captain Amos Burke was suffering from Alzheimer's, when he couldn't remember during the 1990's that he once solved a murder with the exact same M.O. and and a similar suspect with the same motive back in the 1960's.
I don't think mental deterioration would be the cause here. I think Joe Friday, with the heavy caseload he had over the years, must have just forgotten the circumstances. But then again, he was once more dealing with Father Xavier Rojas, the parish priest from that last "case" fourteen years earlier.
Maybe it was now the elder Father Rojas who was beginning to show signs of dementia, and Friday was hoping not to embarrass him by reminding him of what happened in the previous case.
Ho ho ho......