Just about all the studies show weight loss dropping off to or towards zero after about a year or a year and a bit, but not 72 weeks. But that is at a fixed dose. As far as I know there is no real evidence one way or the other that getting to that maximum weight loss dose slowly or quickly changes the total amount of weight lost in the end. There is also no real evidence either way that once stalled at a given non maximum dose that increasing doses works or does not work, but common sense and anecdotal evidence suggests that further weight loss will happen if doses are increased after a stall. I do not think the plateau at a year has anything to do with time as such , it is just how long it takes to get to maximum weight loss on a given dose.
The 72 weeks is just the longest follow up that has been done so far, and shows that the weight loss is maintained for that time if the person stays on the drug at the dose they used to lose the weight.
Without knowing your actual weight and height etc, if you are trying to lose a total of 80lbs, that sounds like at least 25% and likely more than that. Unless you respond extra well, you will probably need to increase doses to 15mg to get that much weight loss.
Losing weight rapidly does have disadvantages, like feeling awful mainly, so it also depends on the current rate of weight loss, how hungry you are, and what side effects you have at your current dose. And if you feel fine or tired and worn out. Making the process tolerable makes it more sustainable long term, and it is the long term maintenance of the weight loss that really matters.
So you probably do need to increase doses to or towards 15mg eventually, but how quickly really depends on the current situation.