Reporting Reported Speech

I think I've found what I had wanted to find, thanks to English Grammar Secrects:

"...when we are reporting something that was said in the past but is still true, it is not obligatory to make the tense 'more in the past'. The choice is up to the speaker. For example:

"The train doesn't stop here."

He said the train doesn't stop here.
He said the train didn't stop here.

"I like Sarah."

She said she likes Sarah.
She said she liked Sarah.

The keyword is "not obligatory", meaning we can write in both ways.