Hi everyone,
Going back to my Arran Carpet example I realised that this species has had a recent txonomic up-date (New Lepidoptera Checklist 2013/2014) when the genus name changed from Chloroclysta to Dysstroma and Arran Carpet became a subspecies of marbled carpet.
So to test whether part of the problem was related to recent taxonomic changes I looked at some fungi where thesome species had been moved from Hygrocybe to Gliophilus. This change was not made in the BMS list which I use on Recorder until fairly recently and was not on the Gateway until last year. 
Fisrt I tried two Hygrocybe species which had not changed - the search work fine but again if I searched on a trinomial I only got the trinomial records, but if I searced on the binomial I all the records were returned.
When I tried two species which had changed from Hygrocybe to Gliophorous if I searched under the new species name although it appeared on the results lists there were no records. If I searched under the vernacular name, records appeared under related searches and if I looked at the original versus processed data the taxon concept id and species id were missing - hence no match. If I searced under the old name there were no results, although in one case Hygrocybe irrigata returned two records both showing matching taxonomic ids in the original and processed data, but these were the old TVKs. For some reason these two records had not been up-dated.
taxon id    taxon concept    species id    
Hygrocybe glutinipes glutinipes    NHMSYS0001484471    NHMSYS0001484471    NHMSYS0001484470    Taxon GUID match
Hygrocybe glutinipes rubra    NHMSYS0001484472    NHMSYS0001484472    NHMSYS0001484470    Taxon GUID match
Hygrocybe glutinipes rubra    NHMSYS0001484470    NHMSYS0001484470    NHMSYS0001484470    Taxon GUID match
                
Hygrocybe virginea virginea    BMSSYS0000008392    BMSSYS0000008392    NHMSYS0001484537    Taxon GUID match
Hygrocybe virginea ochraceopallida    BMSSYS0000008389    BMSSYS0000008389    NHMSYS0001484537    Taxon GUID match
Hygrocybe virginea fuscescens    NHMSYS0001484539    NHMSYS0001484539    NHMSYS0001484537    Taxon GUID match
Hygrocybe virginea    NHMSYS0001484537    NHMSYS0001484537    NHMSYS0001484537    Taxon GUID match
                
                
Gliophorus psittacinus    BMSSYS0000045739            
                
Gliophorus irrigatus    BMSSYS0000045736            
Hygrocybe irrigata    NHMSYS0001484476    NHMSYS0001484476    NHMSYS0001484476    Taxon GUID match
This would suggest that there is a problem where there have been recent taxonomic changes.
Christine