Many of the absent voters in this collection would have been in the military, the Merchant Marine, or the Red Cross. For Armaghthere are about 3,500 names, and for Londonderry about 4,500.
Here’s a typical transcript.
Name John Anderson
Residence Date 1918
Street Address Village of Laurelvale
Residence Place Armagh, Ireland
Registration Unit Mullahead
Polling District Tandragee – S.
Constituency Mid Armagh
Page number 359
In this case there’s a link to the original register with the additional information in a column headed “In the case of Naval or Military Voters description of Service, Ship, Regiment, Number, |Rank, Rating, &c. In the case of other Voters recorded address. For John Anderson that’s “71645 Pte., 36th Bat. M.G.C.”