I thought I came across quotes from the early Watchtowers containing confirmations of Miller's 1843-44 calculations and favorable language regarding Miller. I don't know offhand which WTs that came from though.
If I remember correctly, 1844, according to the WT at the time, was supposed to be a "type" of Christ's birth in the 1st century. I don't remember the particular significance of 1844 which this was supposed to relate to. Since Christ was baptized 30 years after his birth, the modern equivalent was thus his parousia 30 years later in 1874. This was just one of many ways that "confirmed" 1874 as the big year.