it depends on your water...bad thing about ppm is it's not super accurate imo...ppm of WHAT lol... You could have high ppm and no NPK...but if you know the ppm of the input water, and then the ppm after you add nutes, you know how much ppm your nutes add...
Now it is possible that the plant is taking up 100% of N but only 80% of P and K in your nutes...this is why it's important to change your water out completely fairly often (I do weekly, but some do every 2 weeks). But over the course of a week, if you keep the ppm and ph stable I think you'll be in good shape.
When I use input water ppm of about 100, after adding 75% of recommended nutes I am around 700-800 ppm (this is wk 3 of flower). Generally you will want to increase your ppm through your grow until about 2 weeks before you plan on harvesting. Fox Farm recommends 700ppm for seedlings, going up to 1100-1200 throughout most of veg and flower, and then up to 1500ppm (!!!) towards the end of flowering. I think this is WAY to much. I would say 300-400 for seedlings, 650-850 for veg and early flower, and then 800-1100 for mid to late flower.
Best thing is for you to figure it out for yourself. I would add about 65-75% of recommended nutes (whatever you are using) and then check the ppm. If the plants are good with that much nutes, then that is a good level (ppm) for you to be at. As your plant grows you can slowly increase the ppm (by adding more nutes when you change water), but you want to be real careful. Measure carefully and keep notes of how much you added and any signs of stress to the plant (spots and burning).