This story's premise was developed prior to the publication of Half-Blood Prince; it thus completely ignores any canon after OOTP. Canon for purposes of this story consists entirely of the first five books, and ignores other published or unpublished work by JKR, her interviews, etc.
Furthermore, it makes small changes to pre-existing canon in order to get several important plot points to work. For example, we must rearrange events slightly on Halloween 1981, most importantly, precisely when Minerva met Hagrid. The reader who is not closely familiar with the Harry Potter timeline may not even notice these details, but for those who are, I assure you that I am (for the most part) quite well aware when I have violated the canon timeline, and have done so only when I could not find a work-around (you are welcome to suggest one, of course!). Additionally, the calendar has been fitted as best I could to the 'real-world' calendar, including the lunar calendar, and thus certain events (again, for example, Halloween 1981) have been moved slightly relative to days of the week or dates of the year.
Some small, unimportant details (for example, the location of Snape's childhood home) may be imported from later canon, but the plot will for the most part be entirely divergent.
The plot for this story is loosely based on the Severitus challenge; I have described it elsewhere as a meta-Severitus, or "what you might think Severitus was if you'd never run across the challenge". Thus there will be a letter, some interesting parental revelations, and a few of the other standard features of Severitus fics, but it will not follow the challenge closely.
Furthermore, this is attempt to write superpowered!Harry and abusive!Dursleys in a 'realistic' way. If this is not your cup of cheese, please go elsewhere; there are plenty of lovely Harry Potter stories that do not include these themes.
As for brit-picking, my general rule is that I will make substitutions of more British words for American ones if and only if the British word is well-known to me as an American, and does not mean something different in my dialect. Thus while Harry wears trainers, he cooks on a stove, for to me a 'cooker' is at best a separate appliance unrelated to the stove and worse is rarely used as a word by itself. Furthermore, in order to make the timeline work, I have had to make several minor changes to the timing of Hogwarts terms, and thus the British reader is warned that in my universe Hogwarts functions on a semester schedule similar to my own university, in which term begins the first week of September and ends roughly the last week of May; students returned on the Hogwarts Express after fifth year on the 1st of June.
Lastly, you may notice some odd vocabulary choices, particularly in more specialized terms and in the incantations for spells (especially those readers with a better understanding of Latin). I have presumed that in a population relatively isolated from the Muggle world, such as pureblood society, some linguistic drift would occur, especially in the realm of specialized vocabulary. Thus, for example, you will see 'temblor' used where a Muggle would use 'tremor' (indeed, you may notice that Harry uses this alternate term himself); this is not an error as I am well aware that in our world 'temblor' refers specifically to an earthquake but rather an example of this postulated linguistic drift.
All that said, please enjoy the story.