In August 2021 Heinz-Jürgen Kumpf issued "Sinn Féin Christmas Postal Service in Derry and other Parts of Nortern Ireland 1975/76 - 2018/19".
74 pages, in English, coloured, many illustrations of all(!) issues, covers and cards, a lot of background information, excellent(!): Price: about 25 Euro.
Contact and order from *** Private information removed by Staff. Please do not post your address/email/phone number etc. ***
In late autumn 2021 a second handbook was issued by H.-J. Kumpf. This handbook gives information about propaganda and cinderella issues of Ireland. The "Free Ireland" issues should be included, too, as much as I got information from Mr. Kumpf. Price, contact and order the same as above.
H.-J. Kumpf is member of the AIJP (https://aijp.org)
[World Society of philatelic Authors and Journalists]