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are there … systems … heat leading edges that are not fully evaporative?”
Although recent certification requirements have significantly improved aspects of flight in icing conditions, the performance of any system depends on the environment encountered, and possibly the era of certification.
E.g. an older aircraft with a leading-edge hot-air system may be fully evaporative in light to moderate icing (note these are the operational definitions – severe icing is that which the system cannot cope with). The system is identified as ‘anti-icing’, but it has a boost setting of ‘de-ice’ for use when exiting ‘severe’ conditions or with landing flap when presumably the ice accretion can change.
There may be cases where the aircraft is technically in severe icing – the evaporative system is overcome, but the leading edge remains clear, thus there could be runback icing. The certification of this type may have shown (within the confines of the tests) that runback icing in cruise conditions was not a problem, but it may be a hazard during the approach.
Icing operations require a good understanding of the aircraft’s capability and great respect for the environment.
There is good ice, bad ice, and hazardous ice; … good ice is found in the galley.
http://www.ead.eurocontrol.int/eadba...2012-07-26.pdf para 6.3.3.
http://www.faa.gov/other_visit/aviat.../SAFO08006.pdf