HAS diminished or HAD diminished

Try this. http://www.differencebetween.net/language/difference-between-has-and-had/

The journalist who wrote the story used 'has' in error. He or she should have used 'had'. If the direct speech used the present perfect continuous, the reported speech should contain the past perfect continuous, e.g. I am the Prime Minister. I say to a reporter: "I have killed three men in the last week". The report should say "The Prime Minister said that he had killed three men in the last week".

http://www.ef.co.uk/english-resources/english-grammar/tense-changes-when-using-reported-speech/

My golly Pete, Cen, but so wish your Prof weren't Latin. Or is it 'wasn't'

It isn't Latin any more. And weren't is fine.

I see Cen that it's now Chinese
...or is that Japanese

I guess some people just hate English grammar lessons. que sera sera...

Cis, I'd'a' said 'has'

I second that!

Thank you Cis, encouraging in my old age