Hi
I was mistaken in my memory about the annual memorial. Another adventist reminded me it was quarterly for adventists.
However, JWs have adopted many many adventist beliefs, eg just falling asleep when we die...until resurrected. Actually, in my research I have yet to find any teaching that originated or is exclusive to Jws, but shhh...that's their best kept secret which they perpetuate by ensuring their flock lead a very sheltered life.
They are also influenced by Christadelphians, and by the 4the century heresy of Arianism. But yes their heritage is Protestant, except they started hating all other branches Christian religion after Rutherford's coup to take over.