I find the headline fair, after reading the article. The implication of the article is they "could have put" those trapdoors in, since there are primes that ha

I find the headline fair, after reading the article. The implication of the article is they "could have put" those trapdoors in, since there are primes that have actually been widely adopted following their recommendations. BUt if the headline actually read "could have put" then it would sound like an accusation, or speculation. By putting it in the present tense it simply shows that it is possible for this to be performed. It's a very neutral phrasing.