the amount of extra roll you get from upgrading .. the # in the bracket = the amount of time it landed on that stats , which is every +4 upg 

So the spd 10 .. didnt get any upg yet , if its +0 , it could become spd(4) if you +16 a piece

The spd(1) 10 , already has 1 of the +4 upg bonus .. and so on ... if that makes any sense ..

"...if that makes any sense"

I wish it did but I don't know what you mean by "extra roll you get from upgrading" and "which is every +4 upg". 

when you upgrade an artifact, its main stat increases every time you level it up. in addition to that, every 4th level (levels 4, 8, 12, and 16 respectively) you will either unlock a new substat or ungrade an existing one. when an existing substat is upgraded, it recieves a number in parentheses beside it that indicates the number of times it has been increased.

Precisely so :D

Indubitably even.

yea sry , glad someone better at explaining chimed in ;) there a reason i added if that makes sense .. im awful at explaining stuff but wanted to help lol :P