I have found that variations in measurements when degreeing a camshaft is primarily caused by the dial indicator not being "square" or " parallel " with the valve, or not having a flat surface to place the dial indicator stem tip on the valve retainer. Those two items can cause issues trying to get an accurate, repeatable measurement. Regarding the +4. Most cam manufacturers are adding 4 degrees advance in when grinding the cam. It will generally say that on the cam card by stating the cam grind number followed by +4. Lastly, if you use the +4 keyway and marks on the timing gear, it should advance the cam 4 degrees. Naturally, it needs to be verified by degreeing the camshaft in.
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62' Lemans, Nostalgia Super Stock, 541 CI, IA2 block, billet 4.5" crank, Ross, Wide port Edelbrocks, Gustram intake, 2 4150 style BLP carbs, 2.10 Turbo 400, 9" w/4:30 gears, 8.76 @153, 3100lbs
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