To get the concepts down and why shocking is a "process" and not a one time application you have to understand that algae growth is exponential. 1 becomes 2, becomes 4, becomes 8, etc. Maintaining your FC at recommended target levels for your CYA kills the individual cells at a rate that is faster then their reproduction - this means it never really "grows".
The reason for the shock PROCESS is to bump the FC to levels (and HOLD there until you pass all 3 criteria in shock PROCESS) that aggressively breakdown the algae cells at such a rate they simply cannot increase the population in any way and eventually the entire population is dead. It's a chemistry thing, overcome the exponential growth of algae - destroy it at a rate, by time, that is greater than they can reproduce.
Once the population is so small, they can never reproduce fast enough to overcome the levels of your target FC.
If you follow the methods here, never let FC drop or get to min, with accurate testing you will never get visible algae, and if you do you perform the shock process. Visible algae means you need to go through the shock process.
To your ultimate question - YES, algae can grow with your target FC level if the population reaches the point you have visible algae. If you can see it it's already ahead of you and hence the need for the shock process. Maintaining your target FC and never, ever, ever let it get below MIN means you stay ahead of it's growth rate. There are all kinds of organics, algae, cells in your pool (note I say individual cells, they don't last long) - the point of maintaining target FC level is they never get a chance to increase the population and will quickly die.
I just thought of a good analogy. You've got a 1 acre lot and a push mower. The algae is the grass, your mower is the chlorine. You only have 2 hours per day to mow and can do no more (remember chemistry and exponential population growth is based on time).
You have burned your lawn down by following the shock process. But hopefully you keep running the mower over the lawn (by constantly maintaining FC levels) even if you see no grass and it knocks down any little shoots that sprout up. They can't send out runners or do much else as you keep cutting them to the ground.
You fall asleep for a few days and see grass growing, you hit it with the mower but your time is up and 1/8 of the yard has grass. You go out again tomorrow and mow that 1/8 only to find the other 7/8 has grass. So you attempt to mow the entire lawn but the grass is now making you move slower as you're cutting more.
Since you've only got 2 hours to mow the grass is now growing faster than you can cut it, your mower is bogged down and you can't even cut 1/4 of the lawn in your time. Notice you've been keeping your FC levels at recommended levels and mowing the same time, but yet it grows.
Time to follow the shock process. The shock process is a bush hog, in the same amount of time 2 hours but knocks the grass down. You keep using the bush hog and the grass is knocked back to a point it is barely sending up shoot. You go back to your regular mower (target FC).
Yes, algae can grow at target FC levels but it depends on how much there is. The point is to prevent it from having a population that can outpace your chlorine levels.
