Before 2.1, the number in parenthesis was the iLvl of whatever was equipped as your main weapon/tool.

For example, my gear set says DRG (Lvl. 90) 'cause the set was created before 2.1 and I'm using my Gae Bolg Zenith (iLvl. 90). If I were to add the same set anew, now it would say DRG (iLvl Avg. 81), showing what my avg iLvl is.

Updating a pre-2.1 set with new gear won't change the number in parenthesis anymore, you have to create a new set hope that answered your question