You're going to find that specific numbers don't cross from strain to strain, manufacturer to manufacturer, or even specific nute label to label.
To start with different strains of MJ have different feeding requirements and even two different plants within the same strain can vary a bit. Not usually enough to notice, but it can and does happen.
More importantly though is the point that different companies use different methods of solving the same problem - how to get plant nutrients into a good mixture in an easy to use package. There's probably millions of different ways to do the same basic thing and it creates varying degrees of success, quality, and cost.
Certain fertilizer ingredients register "stronger" on an EC meter than others and certain ingredients are "stronger" in terms of being useful to plants than others. So you could have two equally powerful nutrient solutions with radically different EC's because the nutrients in one are more available to plants or because the ingredients in the other are things the meter is more sensitive to, or both.
You've likely noticed that organic fertilizers often require much lower ppm readings than the regular nutrients. Some people point to this as a reason organics are "superior" - you don't need as much. But in truth organics are just harder to pick up with your EC meter. The plants are eating the exact same stuff and the exact same amount of it. It's just harder to detect.
I prefer
Advanced Nutrients myself, I like the consistency I get from them. Plus the "right amount" of their 3-part in EC is the same "right amount" of their Sensi 2-part so once you get things dialed in with one AN product it's pretty easy to move around in their feeding schedule. (Of course their organics are still different target EC's.)
Play around with the calculator they've got sometime and you can see what I mean. You switch between most of their base nutrients and the numbers stay the same, but certain other ones are totally different. Same company, but certain of their nutrients still register differently on the meter.
