Hmm it's all relative. "follow the instructions" because Plagron are right about most things. No need to supplement ca/mg with coco A&B. If you use hydro A&B with coco you need to supplement Mg. GS is quite strong, half dose is OK
if I plant seeds here and give them tap water for 14 days, I will for sure be looking at a bunch of crippled plants with drained cotyledons, deficiencies and yellow leaves. But thats because mine get a lot of light. If I put them in a low light situation yeah you can get away with things.
Wouldn't worry too much about it, just satisfy the medium and see where it goes. The plant takes what it needs. If you make feed water 1.2 EC, run enough water thru the coco so the drain EC is the same as input EC, you have effectively set your coco EC to "light mix" levels. Even a monkey can keep plants alive for 2 weeks in a light mix (peat), which all target approx 1.2 EC. With the coco set to 1.2 EC you can put a seed in there and it will grow well. I set my coco to 1.6 EC then I put seeds in, then they grow, and then I smoke the weed.