Are my cats underweight?

I have a 5-year old female Ragdoll who has always been a bit small in frame.  I also have a 4-year old male Singapura.  They never had food problems until about 4 months ago.  My cats could eat about anything and they did well.  

About 4 months ago I switched to a new dry food and it was a really bad mistake.  They began vomiting and lost weight.  I tried to switch back to the old food, but they still vomited that food now (more the Ragdoll than the Singapura....he seemed okay when I switched back).  The Ragdoll went from 14 pounds down to 9.  She couldn't hold anything down.  I took both cats to the vet, and tried a new food, a soft food (Wellness, Turkey) and they were fine with that food.  

Both cats have gained back some but not all of the weight, and they never vomit now.  But the Ragdoll is now around 11 pounds and eats well, and the Singapura is still about 1 pound lighter than before this all happened.  He's about 6.5 pounds now.  They eat well, like the food, and seem healthy and active.  But should I be worried that they never returned to their dry food weight?  I took the Singapura to the vet over the weekend for his annual shots and checkup, and the vet noted he was about 1 pound lighter than a year ago, but didn't seem concerned.  But I do worry.  Why didn't they get back to their previous weights?

I wouldn't be too concerned.  As long as you can't see their bones protruding, I'd say they're good.  If you're concerned you can always ask the vet.  Since you're feeding them a grain-free wet food, they aren't getting all the carbs from the dry.  Also, they shouldn't eat as much because it's all protein and their bodies process that more effectively.