Oxford Library OLIS has 85 Clifton songs catalogued online and available for inspection or purchase of copies. Some are in multiple copies and a few are duplicated in the 85.
They are part of the Bodleian Collection pre 1920 Catalogues, either in the Harding Music Collection or in Music Vol III.
Go to the search and bring up authors then enter 'Clifton, Harry'
Useful for serial numbers, dates, lithographs and first lines, etc.