If Denethor hadn't committed suicide

[Formendacil]

Originally Posted by Inziladun

If he claimed anywhere in Gondor as his origin, that claim could have been investigated. I can well see Denethor 'checking Thorongil's references', perhaps with the hope of catching him in a lie.

Perhaps Denethor did search Gondor...

...and that's why he was extra-suspicious of Thorongil's origins, when no one else seems to have been. And what could Denethor make of it, if Thorongil was from the North? That's no reason not to serve Gondor or be untrustworthy... but, if Denethor's suspicions were right, and Thorongil was making a play for the throne, revealing that he was Arnorian might be the first step to Thorongil revealing he was the Heir of Isildur. Far better, in such a case, to abet the idea that Thorongil was from an obscure corner of Gondor--Andrast, maybe--than to put the idea in people's heads that Thorongil could actually supplant him.