Strange but I have never given this matter a thought until you raised the question which has, in turn, prompted me to take a look at the contents of my jacket wardrobe.

My Montrose Doublet (dating from 1968) has the buttons sewn on randomly - except those on the sleeves, which are sewn horizontal to the cuffs.

My barathea Crail jacket (1999) has all the buttons sewn randomly.

My Prince Charlie (2001) again has the jacket buttons sewn randomly and the sleeve buttons sewn horizontally to the cuffs. The three on the waistcoat are also placed horizontally.

My GT Doublet, a single-breasted Montrose, (2005) has the jacket buttons sewn randomly and those on the sleeves are again horizontal to the cuffs.

Since all four jackets came from entirely different Highland Outfitters in Scotland over a period of years, I have to assume that there is no regulation method of placing them. Were I wearing each jacket as part of a uniform, say in a Pipe Band, then I would like to see everyone's buttons the same way, but otherwise, for myself, I am not in the least bothered.