The phrase "all of which warned" is correct and usable in written English.
It can be used when referring to multiple subjects or items that provided warnings or cautions about something.
Example: "The reports were concerning, all of which warned of potential risks associated with the new policy."
Alternatives: "each of which cautioned" or "all of them alerting".
Investors seemed to shrug off dire warnings from the Organization for Economic Cooperation and Development and Moody's Investors Service, both of which warned that the euro zone problems were well on their way to becoming serious issues for noneuro countries.
Richard Lloyd, executive director of Which?, warned that the UK's energy market was "broken", because of too little competition among the big six suppliers.
The app received many poor reviews from upset users, plenty of which warned others that this was not the app they were looking for, but that apparently didn't stop people from downloading it.
More than a decade before the June 4th Massacre, right after his Reform era began, came the "Democracy Wall Movement" -- named for a Beijing area where critics started putting up posters (some of which warned of Deng becoming a dictator) in 1978.
The car's developers chortle over the owners' manuals of other hybrid crossover vehicles, most of which warn against venturing off pavement at all.
Half of all TVRs during the study period evoked negative emotions, including all those which warned of the negative consequences of smoking (Table 4); 45% evoked positive emotions.
A decade later, he produced another work called The Three Lies of Painting which warned viewers of the dangers of its own genius even as it seduced them with it.
The quest for stronger, more coherent standards dates back to the iconic "Nation at Risk" report of 1983, which warned that "a rising tide of mediocrity" was jeopardizing the country's future.
Any export deals by the Greek Cypriot government in Nicosia will risk the ire of Turkey, which warned during recent bailout negotiations that the Turkish Cypriot northern part of the island should share in any exploitation of natural resources.
New Zealand-born film-maker Jane Campion, director of the international award winner, The Piano, returned to Cannes this year with her short film, The Water Diary, a lyrical, child's-eye view of drought which warned gently against global warming.
