Ian - thanks for the clarification.  Yes, it IS a bit complex, and an unusual way of doing this sort of analysis.  Using the much simpler way of extracting just the number of species trapped, and not abundance, I can see that 2007 and 2012 were indeed poorer than other years within my own records, but as I recall, these were exceptionally wet summers, and made a distinct difference overall, but 2016 was as good as most in my trappings on this basis, even though I think that too was not good weather-wise.  Still, it helps to pass the dark days - all good fun !!