Random Thoughts:
I am not speaking about the A-B lights; but from what I have read about the generic Diesel Timing Lights You have to already have your Fuel Injection Pump timed correctly.
Hook up your Timing Light and see what it does.

Once you have the specs you can now use them the next time you use your Diesel Timing Light.

As far as Drip Timing not being accurate; at least in the past all most all inline Fuel Injection Pumps were Drip Timed (Flow Timed). The exception is where some companies use a Timing Pin (CAT does this).

When an inline Fuel Injection pump is rebuilt each one of the Elements is drip timed to the proper degrees of Fuel Injection Pump Camshaft rotation before the Pump is calibrated. The exception is where some companies specify a Dial Indicator or Depth Micrometer reading ad such-and-such Camshaft position (CAT does this) on the Element Plunger.



The inaccurate part of Drip Timing comes from the manuals not being entirely detailed about the procedure and not keeping a constant Fuel Supply pressure.

Also it requires a little understanding of what is going on inside the Fuel Injection Pump concerning the Begin of Injection how that is related to the x number of drips per second when you time it.

And, then there is that it may just take some practice.

I think another problem with doing a Drip Timing for the first time is that people simply rotate the Fuel Injection pump too far or turn it the wrong direction and sort of get lost for a while (put some reference marks before you rotate the Fuel Injection Pumps so you can get it back close to where you started).
Assuming that your Fuel Injection Pump is a few degrees late in timing due to Timing Chain/Gear/Stretch/Wear the Fuel Injection Pump only needs to be nudged a little bit in rotation to bring it back into timing.

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84 300D, 82 Volvo 244Gl Diesel