A look back at the first post shows that the original question appears to be in general and not about a specific type. Despite claims that it is only from a Boeing point of view, that original poster may go onto other aircraft. Other people reading this thread may be on different types and when they read from a supposedly experienced type that ice is NOT going to happen below -40, they may believe it.
Examples are given showing that engines have been flaming out and aircraft involved in serious incidents much more than previously thought, yet the accusation is made that they are from "dodgy accident connections and theoretical papers" even though a Boeing magazine is quoted.
Then it is said that in 38 years of flying, icing below -40 has never been experienced even though this thread is about unseen icing in engines from ice crystals that don't accumulate on the airframe. 99% of us or more have likely never seen such icing either.
I am going to post a link to perhaps another dodgy accident connection. That is the NTSB. It talks about several of these incidents. One of them, a Beechjet was at FL 380 with a static OAT of -57°C as read in the actual accident report.
http://www.ntsb.gov/recs/letters/2006/A06_56_59.pdf
I think the original poster and others have more than one thing to learn about on this thread. One from a technical point of view and another from a human factors point of view on aviation hazards. And remember, what happens on one aircraft can be much different to what the same effect does to another aircraft. Also remember remember that over the course of your career you will receive much false/misleading information from others that you talk to.
Here are some quotes.
"The Safety Board is well aware of the threat that ice crystals can pose to turbine engines. On June 4, 2002, Spirit Airlines flight 970, a Boeing MD-82 airplane,15 experienced a dual-engine flameout of its Pratt & Whitney JT8D-219 engines after high altitude ice crystals blocked the engines’ inlet pressure probes while the airplane was in cruise flight at FL 330."
"During the investigation of the dual-engine flameout events, it was learned that a general perception exists among flight crews of airplanes that fly at high altitudes that ice is not a threat at the higher altitudes because it is “too cold.” This perception is reinforced by the fact that the ice crystals that are of concern do not accrete on the usual places that pilots look for ice such as the wings, windshield wiper blade arms, or the arm retaining bolts."
"The Safety Board notes that the problem of multi-engine losses of power due to icing is not limited to the JT15D-5 engine and that General Electric CF6-80 series engines have also experienced in-flight losses of power due to internal icing.