One of the things about Republic of Ireland notes is that they are relatively scarce in grade 66-68. The issues stopped in 2001 when the country joined the Euro. £50 and £100 were relatively large denomination notes, and while £50 notes were circulated through cash machines, the £100 denomination was not. The only way to obtain £100 notes in UNC was to to them from a bank.
Imho, the PMG populations of Republic of Ireland notes are not a reflection of what is out there, very few Irish notes have been graded, relatively speaking - few Irish collectors go for it, and just dealers who trade abroad seem to submit notes fro grading, from looking at notes at shows.