I noticed a lightening bolt mark over many abbreviations that looked like Harry Potter's scar. Would it not be a hoot if this is where Rowling got the lightning bolt from rather than from runes? I do not know what this mark represents but I do know what all those 7's that I saw were: the Tironian shorthand for 'and'. Tiro, Cicero's slave and secretary, did not invent the ampersand, that is the '&'. Using '7' for 'and' was not a problem in Roman times since they wrote seven like this 'VII'.
I am familiar with one other bit of Latin shorthand, although until recently I did not know it was a Latin abbreviation, and that is 'Rx' for prescription drugs. That R with the slash on the leg that looks like an 'x' stands for 'recipe', which is the imperative form for 'recipio, recipere' and means 'take'. Back in the old days when paper or parchment was expensive and hard to come by, people tried to squeeze as much as they could onto whatever paper they had. Ingredients or directions for medicines always started with the instruction 'take' and so the abbreviation was common on prescriptions since they all started in the same way. As I keep saying: you know more Latin than you think.