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Simply put a VACUUM/FUEL PRESSURE gauge on the dipstick tube. That will tell you if there is a partial vacuum or a pressurized crankcase.
A PCV Valve is not a precise piece. The OEM was calibrated for a specific engine(s) and was calibrated to work with several. The fuel/IGN curves were modified to work with whatever valve. As the engine wore/lack of maintenance, the system failed. Modify manifold vacuum with a cam or never adjust the valves and it will throw off the OEM System. That and the early designs were not that concise.
There are also not as many valve applications as there once was. Many have been deleted and/or replaced (the one fits all and CHI-COM).