Exceptions to Backshifting
"In certain situations, the sequence of tense rules are relaxed and backshifting is not required. Essentially, backshifting is not required if a statement about the present or future still holds. . . .
"A shift is not necessary if:
- the original statement is a general truth.
Torrecelli concluded that the atmosphere is/was a sea of air pressing down on the earth.
- the speaker is reporting something that is still true.
Fred said he drives/drove a 1956 Belchfire Special.
- the speaker is reporting something still possible for the future:
The forecast said we will/would be having lots of rain.
- the speaker repeats something he or she just said.
John: I like opera.
Bill: What did you say?
John: I said I like opera."
(Ron Cowan, The Teacher's Grammar of English: A Course Book and Reference Guide. Cambridge University Press, 2008)
"Backshift . . . is optional when what was said applies equally at the time of reporting: Benjamin said that he is/was coming over to watch television tonight. Such traditional shifts are not, however, used in certain types of relaxed, colloquial reporting and storytelling: Then he says he's coming and she says that he could come or not for all she cared."
(Tom McArthur, Concise Oxford Companion to the English Language. Oxford University Press, 2005)