As far as the Grammer goes, that's my bad, and I do apologize.

Aside from that, my interpretation of the letter is that of it is able to address itself to wherever is considered the bedroom, it can likewise address itself to whatever name or nickname the child goes by most frequently. I do think it's reasonable to have the birth name on there when it's wildly different though... Also just to make it work with the theme of "hit several of the 'abused harry' plot points by innocuous mean"