I've had a kerbal in a decaying orbit for some time now (I lose about a meter to my apoapsis every 3 seconds), with an apopsis of ~80km and periapsis of ~67 km. I've made a few rotations around Kerbal, but my 'Achieve orbit' contract has not gained a check-mark. My orbit has since decayed, as seen below, and I expect I will not complete the contract despite several successful rotations around Kerbal.
Am I failing to meet some hidden criteria? What are the exact criteria needed to complete this contract?