Closed throttle DOES make the resulting reading lower!!
Frankly, even-ish reading between cylinders is more saying "general wear" than a cracked ring (then one cylinder is dramatically different). Or head gasket failure - that's typically uneven pressures.
Looking at the original question: Oil lost.
1) Is there OIL in the ANTIFREEZE??
2) Cardboard under the car - Oil puddle anywhere??
50 years from now - how are we going to restore a "classic" microprocessor based modern car?? Alfas - 1980 Spider, 1987 Milano, 1976 Spider