Guild Wars 2

Have two Sylvari, one medium and another heavy. I previously bought 2 armour pieces for my medium which were listed as 2/6 in the achievement and recently bought 6 items of armour for my heavy but the tier is listed 6/12 but shouldn’t it be 8/12?

Ive checked that I have all the armours and can only say that I bought the last 6 in quick succession if that makes any difference.

Never mind just realised it counts 6 only for each tier of armour….good thing it was only tier 1