You explained perfectly!
It's what i call a "merry dance" lol
"When nutrients mess me about!"
You'll soon get used to how to build up your EC and be able to mix the right amounts quite easily - it's just a pain in the arse to begin with (especially if you're trying to up the EC by 0.1 every time (which i have and its a pain))
You need to use your best judgement a little bit. For example if i mixed my feed a bit too weak on day 30 .. i would be adding a bit of A&B to build it up.
If i did the same at day 60 - i'd add a little more flowering booster (synthetic) to up the EC (not CANNA Boost becuase it doesnt have an EC). but you could easily build it up with A&B .. i just find one bottle easier than 2 lol
Also you need to know what your bottles are doing as you mix them in.
I tested after every addition to see what was happening and it's a good idea.
Rhizotonic will not add EC but will raise PH
Boost will not add EC (cant remember what it does to the PH)
EC check after every addition (you'll probably only ever do it once or twice) and you'll get the idea!
Blue ^_^