PCV = Positive Crankcase Ventilation: one-way ventilation of the crankcase through a check valve, venting vapors only when the crankcase pressure is greater (positive) compared to atmosphere. Later variations vent the PCV to the air filter housing upstream of the filter, at atmosphere pressure, to capture the undesired emissions (and burn them through combustion).
CCV = Constant Crankcase Ventilation: constant crankcase ventilation, at all times with ported manifold vacuum to the crankcase, to always keep the crankcase negative to the atmosphere. A negative crankcase pressure better contains the undesired emissions, and the constant manifold porting of the vapors better assures these emissions are captured (burned through combustion). The filtered CCV make-up air also works better to keep the internal surfaces of the engine clean.
The factory 0.10-inch CCV manifold port works well for a new engine, although may fail to flow enough volume to maintain the negative crankcase pressure in a worn engine. The solution is to provide a greater volume of ported vacuum from the intake manifold to the valve cover (a larger metered port), and make sure it is clear of obstructions.
When I purchased the Wife's 89 XJ the CCV tubes were clear (a receipt was in the stack reflecting the retrofit tube kit) but the fitting on the intake manifold was plugged shut. Cleaning the manifold fitting and opening up the nylon port fitting (to 0.1875") stemmed the oil purge flow. The larger tube going to the intake hose will stick to your finger from the suction (the easy test). The XJ still has 155,000 hard miles so the oil leaks also needed attention, and the valve cover oil fill cap area needs cleaned every few thousand miles, but there is little oil in the filter.