Moving to tongue in cheek mode - Oh to be a fly-on-the-wall in the meeting room where RR are holding their forensic investigations into the decision stage on the FOHE design. Why that design, why not the GE or P&W one? Were the GE and P&W engineers just lucky or did they have knowledge that guided them, and if they did, was this available to RR? I've lots of follow-up questions but will spare you.
There is a lot to be learned about how the industry shares knowledge and, probably more crucially, the authorities must determine how it is that, this most technically advanced global industry, does not know how fuel behaves below -18C.
I think that you need to keep in mind that this is not an engine design problem under regulations Part 33 (engines) but an installation issue under part 25 at the airframers. Considering that the understanding that we have today was not known by the regulators who approved the system, then you can assume that it wasn't recognized as well across multiple manufacturers.