So there are two Shiawase Relation books here, but they seem to tell the same story. What gives? Here’s a bit of extra context.
tMnR originally published this doujin in 2015. One year later, she went back through the book, intending to only correct the bits that bothered them. (E.g. Clunky sentences, awkward phrases, and the like.) That idea quickly went out the window. tMnR decided to overhaul almost all the dialogue, then added another 9 pages for good measure. If you compare the two, you can see areas where some of the artwork was tweaked or completely redrawn. She released this updated edition in 2016 with a slightly tweaked title. (The old one was called 仕合わせリレーション, while this one is 仕合わせRe"lation.)
Basically, think of this as version 2.0 of the original Shiawase Relation book.