I always thought that the elliptical conditional clause "Had + Subject + past participle" is used only in counterfactual conditionals, e.g. :
Had Joe seen Mary, he would have fallen in love with her.
Recently, however, a number of native speakers said the boldfaced part in the following is okay:
We retreated to the car while Marco kept apologizing for the rudeness of the twins to our hosts, whose gazes were now anything but friendly, had they ever been.
I'm confused. The above is not a counterfactual sentence. Can "had + subject + past participle" be used in non-counterfactual conditional sentences? Do those native speakers (NS) have a poor grasp of conditionals?
For some examples of how NS find it okay in non-counterfactual conditionals, see Quora, and the reply by Mike Pattison.
Your sentence seems unnecessarily complicated, but your question is about choosing between two conditional clauses and on that basis alone, either is acceptable. Personally, I would have said “if ever they had been” as sounding perhaps more natural, but that’s possibly a distinction without a difference.
From The Free Dictionary Language forum, the reply by FounDit.
Yes, it's correct, but I'd say it's also very formal wording. It conveys the idea that the hosts never truly had friendly gazes, and they certainly were not at the point of leaving.
And https://forum.wordreference.com/threads/apologizing-for-the-rudeness-of-the-twins-to-our-hosts.3994987/ , see post #5, where Cagey says the sentence is "fine."
But then there is at least one native speaker who thinks the sentence in question is wrong:
See ELL, where Michael Harvey says, "It's wrong, it's bad. That's all. Replace with 'if they had ever been'" in the comments.