My parents had established a mineral trust in 1986. At that time there was no value in minerals. So no gift tax paperwork was completed. The trust designated 50% went to them and the other 50% was split by 5 kids. In 2006 they leased out their mineral acres for 5 years. In July of 2010 they redid their trust lowering their share to 2/7 and the rest of us kids received 1/7 which increased each kid’s share by 4.2%. In September 2010 they top leased mineral. Since the trust was changed in July what gift value is associated to the kids now that the share is larger? Would it be the current mineral lease that was in effect when they redid their trust or the new top lease that happened in September? Thanks.