There are around 7 species of Coleosporium (mainly host-specific) which are shown as valid taxa on the NBN Atlas, but which can't be entered on irecord as they are regarded as synonyms of Coleosporium tussilaginis. I don't know why there is a discrepancy between the 2 systems both based on the UKSI.
The NBN Atlas has been updated with recent UKSI changes, but iRecord doesn't appear to have had the species dictionary updated for some time. I assume there is atechnical reason why it hasn't happened, but I find it frustrating too so hopefully getting it sorted so we can record recent additions to the British list, recent splits and use the most uptodate taxonomy is a priority.