The list was announced in March, 2016.
Good catch.
I mistakenly put 2016 instead of 2015 as the date. Clovis joined the Trump campaign in August 2105. Clovis was already interacting with Papadopoulus and Page then. Papadopoulus had been with the Ben Carson campaign, Clovis with Rick Perry.
Sessions endorsed Trump in February 2016.
If Pap was an informant or plant, there was probably spying on Carson.