It doesn't work like that.
three +1's = one +2
three +2's = one +3
etc. BTW nothing happens to +5 parts once you get 3 of them and use a coupon. BC used to have +6 parts but they got removed.
three +1's = one +2
three +2's = one +3
etc. BTW nothing happens to +5 parts once you get 3 of them and use a coupon. BC used to have +6 parts but they got removed.