I have tested with Family Tree DNA, MyHeritageDNA and 23andMe but after 2017. I'm also waiting for Ancestry results.
All my 16 GGP are known (as long as none of them are NPEs) and are all supposed to be Icelandic.
There is some strange strong connection with people of American Colonial descent that I'm still trying to figure out but all of the suspected possible NPE slots are at 3rd GGP or farther back... or so it seems at the moment.
My GedMatch numbers are WN7164845 (MyHeritage/ftDNA), NM3613622 (23andMe) and CR940901C1 (Superkit).
Sigurdur Jonas Eysteinsson