The answer to this is yes and no, replace like for like hair lost, no, but have the cosmetic illusion of a full head of hair, yes.
As hair loss progresses it becomes harder to treat the surface area; high Norwood Scale hair loss sufferers, NW6-7 may not be able to achieve a full coverage, dependent on the quality of their donor hair. As it is impossible to replace like for like hair a hair transplant procedure relies on artistic and medical skills to achieve the desired coverage and look of density or fullness.
If hair is spread over the recipient area in a diffused pattern although coverage is achieved the result never looks natural or cosmetically desirable, a minimum density of hair is required to block the light from reflecting off the head. A Master Plan is required to ensure that if hair loss progresses a balanced coverage can be achieved, fixing a low aggressive hair line may seem a good idea initially but if the coverage cannot be balanced it will look unnatural.
To achieve coverage on a high NW candidate will require 6000 plus grafts or follicular units from hair line to crown, dependent on hair line placement and hair characteristics of the candidate, but not everyone can reach these numbers.
The appearance of thickness is also aided by the placement of the follicular units, the angle and orientation and the curvature of the hair shaft following the natural lay of the hair. Placing the hair at the correct angle can increase coverage and block reflection of light off the scalp. Watching the hair curvature allows each hair to blend with the adjacent hairs more effectively and naturally. Especially when treating relatively minor hair loss it is important to try to access the possibility of advanced hair loss, obviously this is difficult, especially on younger candidates.
Before deciding to undergo a hair transplant research thoroughly, become hair educated and do not always believe what you want to hear, base your decision on facts and logic.