Genghis, et al; some aircraft have a combined engine intake lip and first stage compressor anti icing system. The146 is an example; the weakness of the compressor element contributed to the ice crystal problem.
The anti ice OFF situation was considered. In ‘theory’, the ice would bounce off an unheated blade / stator and proceed to the ‘hotter’ parts of the engine without problem. However, in this, there are at least two considerations. First, that the air entering the engine and compressor is heated by ‘intake’ compression and thus the first stages could still accumulate ice – note that some engines suffer fan blade icing in similar conditions. Second that in other circumstances not far removed from ice crystal conditions, the IWC of the atmosphere became liquid (and/or super cooled) before entering the engine, again leading to the possibility of icing. The research suggested that an altitude change of 2000 ft below the ice crystal layer might be sufficient to cause this – a change from an unknown problem to a known problem, but each requiring different anti-ice system selections and the crew not having sufficient information to decide which.
Thus for the 146 there was a need to need to fix the root cause - modify the engines; then follow the manufacturers procedures – use anti icing.
The absence of specific procedures/advice in other aircraft (IIRC the 146 has none) may reflect that other manufacturers heeded the research information and modified their engines (search for ADs), particularly those with evolving designs. Manufacturers still rely on ‘airmanship’ for the avoidance of Cbs by a sufficient margin – but what is ‘sufficient’.
Note that the 100+ events appear to be on Boeing aircraft only; I don’t have figures for any others except that the 146 had 50+ and that engine manufacturer’s shared data of events was a very (disturbingly) large file. Obviously, this excluded non-reported or misidentified events, and any that were incipient, ‘close to the edge’ and not seen by the crew.
Perhaps of interest a ‘what if’ question was asked about the use of airframe anti-icing in ice crystal conditions. Did the ice melt, runback, and refreeze in a more hazardous position. At that time, there was insufficient evidence for any practical operational conclusion.