Interesting piece below on the liturgical history of the connection between All Souls Day and the Office of the Dead.
Source is: https://sicutincensum.wordpress.com/2018/11/04/sundry-remarks-on-the-history-of-the-office-of-the-dead/
Excellent article and blog, but it made me realize that I made two mistakes yesterday

I pray the Little Office of the Blessed Virgin Mary every day. Yesterday I prayed the Office of the Dead but I didn't know that it was supplementary, as this article says, and I skipped matins and lauds of the little office. Also, I didn't pray vespers of the Dead on November the 1st but on the 2nd.
Which makes me wonder... if I want to pray the office say in the anniversary of burial of some Christian, do I have to pray vespers the previous evening?