Several sources I've looked at suggest quite different standards as well.
I arrived at the 4.99 grams from the reef side (namely ReefCentral folks)which tend to be anal about such things.

Using something other than baking soda(heat CO2/water issues) might be tougher to dissolve, but would not entail as much errors in other areas.
I asked Greg Morin and there's some discussion on various reef forums.

I'm looking at other standard base chemicals to get the bicarb HCO3 other than baking soda for a KH solution.

I have not gotten around to it, nor the pH membrane probe test either, but in due time I will.

Regards,
Tom Barr