yes correct,you add all together and number increase,BUT what size are your volume? get it,if a 40 lbs bag of 0-46-0 is that it is from 40 lbs of volume,so 1 cup wouldnt equal 46 right ,if you bought say 4lbs of each of what you describe ,all containers the same and you use all the products for your mix your numbers be dead on.
hell ya add mycos,always the best,all im saying is by combination of what you mention,what is the real value,only isolated test would be correct if you dig,and if it were that easy and did work that way it would be so concentrated you couldnt add that much,if you dig,so what ive done over the years is a basic start.
get several samples of the soil in all difrent spots,combine and mix well,get out all debri ,sticks clumps and shit like that,anyway fill your jar 3/4 full with your soil,fill jar with water shake it for 1 min,set jar on a level counter top or window ledge,wait 10 min,down on very bottom be a sand line,you will see it,take a black marker make a line on jar were the sand line is,wait a hour and you will see your silt line,do the same with marker,wait 24 hours and do the same with clay line,ok from there take the water and do your NPK testing with that water,this is when you really know what you have and were to amend in whats needed if you dig,before you dump out the soil you used before the jar test take a little and do your ph test ,so all bases are covered.it would be nice at this point to be able to just do as your mentioning of adding the numbers,but not real.
so if you want to amend extra stuff after all this testing is done,and have figured out your value correct,more than likely your ph is gonna swing high from the add ins,mine is always higher ,i do outdoor veggies and indoor medicine haaha the main reason i keep check on texture is from watering with 200 ft of hose and dont have energy to water every day hahahah,inside the tent i go with lighter mix of texture,more silt were i can feed more often,outdoors my mix i only feed every 2 weeks,to much work playing fireman hahahah,anyway probally confused you,have myself haahah,but if your great with math all that you mentioned can be done on smaller scale as you mentioned,im just a old guy that was born to work a farm and didnt have school ,so always shoot from the hip if you dig.
here is a example the bottles of nutrients you buy,the math is broke down to what the bottle says for NPK,it is concentrated were all in all about 1 tbsp of all combined nutrients in the bottle the rest is water