Apron shaping is one of those things that is hard to explain and impossible to give firm rules about.
A lot depends on the shape of the kilt wearer. Some will depend on how the kiltmaker learned their trade.

Rocky makes a kilt that is different from the way Barb makes them. You are comparing apples and oranges.

I am about in the middle. Some of my kilts are made with the extra on the right and some not. It depends on the shape of the wearer and is sometimes due to the fact that some of the fabrics I use have different properties.

As the apron should be about 1/2 of the waist measurement arbitrarily adding to that may make the aprons too wide. The apron edges will flap around wildly as you walk.

Simply adding as you state would also make the hip measurement too big. This can cause the back of the kilt to hang in stage curtain waves instead of a smooth flat surface of pleats around your butt.

The 1" added to the right side of the outer apron as explained in TAoK is due to a tendency of the outer apron to appear to hang shy of the under apron right edge because it is outside of the under apron and must travel further. You can think of it as an illusion or kiltmaker's trick to make the aprons appear equal.

If this is your first attempt at kiltmaking I would follow the instructions in TAoK exactly. Then before you cut away the pleats try the kilt on. You can correct anything in the fit or hang at this point. You can even un-stitch the entire kilt and start over if you wish. Just remember that the bulk of the pleats will still be there and the kilt will fit snug or seem too small till you cut away the pleats.

Once you have the kilt completed and have had a chance to wear it a few times, then you can make corrections to your measurements card.

You may want to widen the amount of taper if you experience 'pleat kick'. You may want to adjust the splits if the aprons are not 1/2 the waist. etc.

The most common cause for the waist measurement coming out different on the kilt that what you have on the card usually has nothing to do with the measurements but in how accurately you stitched the pleats.

Remember that if you have 32 pleats in a kilt and you get the width of each on off by only 1/32 of an inch the final size will be off by a whole inch. 1/32" is about equal to 1/2 of a twill line in 16oz fabric.

To measure the waist size of the kilt use a tape measure and lay it along the kilt from the right side of the outer apron at the level of the top straps. Work across the kilt staying at the level of the top straps until you get to the right edge of the under apron. This should equal your waist measurement.