Hello
@Moko, on average someone is likely to have two hair transplants over time. But, some may have more. At the same time, you can collect anecdotal evidence. It´s best to try and look at similar situations to yourself: your age and family hair loss history for example. Also, whether there will be long-term use of a hair loss treatment. Or maybe no treatment use at all. For instance, if you have a hairline reconstruction in your mid-twenties and there is a pattern of hair loss in your family, albeit not particularly advanced. There is a greater likelihood you will require at least one more hair transplant at later date.
As a result, planning is important. The use of a hair loss treatment is generally recommended. But it is elective, as is a hair transplant. Some decide the treatment is never going to be used. Subsequently, this needs to be figured into the planning. As well as ensuring the donor is capable of treating more advanced hair loss if required. That the hairline design withstands the aging process. Framing your face well at the time of the procedure. But also as you age. It still complements your facial bone structure.