Just to be certain, there's no other reason that the fuel flow from the drip tube would cut at at that point--like from an injection on one of the other cylinders (but, those should only happen at another 360 degrees of crank rotation for #3 and opposite for #s 2&4, right?)

If you do not keep the Fuel Supply Pressure up and somewhat even the number of drips is going to be different.
If you are using the Hand Primer to keep the Fuel Supply Pressure up I have often advised to let someone else do the pumping of the Hand Primer while you do the Fuel injection Pump Twisting and Drip counting.

After the begin of injection I have no idea how many degrees the Feed Hole in the Element is covered.

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84 300D, 82 Volvo 244Gl Diesel