How much can be actually be harvested with FUE?

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Hi all, this question has been answered countless times across the internet... but with wildly varying answers. I'm hoping someone can explain the variation, so I know who to trust.

I'm 30yo caucasian (wavy black hair), and my surgeon (Dr. Diep) did a 2700 FUE procedure on my front 30-35%, and I'm currently figuring out whether to go back and use 500 more to fill in a sparse patch that didn't grow super well.

He said that people (including me, with average density) should have 8000 harvestable by FUE (close to 10000 if only FUT, 12000 for FUT+FUE) total over their lifetimes. However:

• This 2016 textbook "Hair Transplantation" says "The safe zone for FUE is wider but since only some units can be extracted from this wider zone, FUE extraction of grafts beyond 4500-5000 from the permanent zone usually may have issues like thinning donor area and visible FUE scar marks".
• In http://shapiromedical.com/procedure-...ntages-of-fue/ says "new paradigms for FUE graft harvesting plus the use of bio enhancement products like Acell & PRP to stimulate new hair from the donor area has slowly increased the number of grafts obtainable from FUE. At the time of this writing this subject is very controversial but most physicians believe that one can get more grafts with Exclusive use of Strip FUT (6000-9000 grafts) than Exclusive use of FUE (4000-5000 grafts)."
• In https://www.realself.com/question/al...fue-donor-area Jae Pak says 6000-8000 and William Rassman says 6000.
• Follicular Unit Extraction: Evolution of a Technology (2016, Rassman, Pak, Kim) says "Assuming 10,000 FUs exist in the donor area in the Caucasian example, the maximal targetable harvest limit should be ~5,000 FUs." and "FUE performed in excess of 5,000 Follicular Units, depletes the Caucasian donor area significantly." Though this was talking about an example person with 10k donor FUs.
• https://newhair.com/resources/#tab-id-4 (Rassman, Pak) says 3,450, though it's talking about a type VII donor area.
• Estimating the Number of Lifetime Follicular Units (Unger, 2013) Says for 30yo caucasian, 5,393 for average type VI, though it doesn't specify FUT vs FUE. Also, it's since been taken down, and the methodology was suspect (surveying 39 doctors by asking questions, and huge margins).
• In https://www.alviarmani.com/hair-tran...ransplant-faq/ under "Can I undergo more than a hair transplant?" says "The potential number of implants that can be extracted from a person is around 8000 grafts or about 16,000 hairs."
• In https://www.baldtruthtalk.com/thread...-Area-Question John P Cole says that he's taken up to 9500 with FUE.
• In Assessment of Safe Donor Zone of Scalp and Beard for Follicular Unit Extraction in Indian Men (2019) it says that Indian people can (over two procedures) pull 50% of their donor area for a total of 6184 in areas 1+2 (but 7,224 including extended) for FUE. (Note, I'm not Indian)

I asked Diep about these varying numbers, and he said that:

• the lower numbers are probably out of date,
• the people online aren't actually doctors,
• If you read medical papers, it's 8-12k,
• It really depends on who's doing the surgery, and how efficiently they can get it out.

I asked him if he could point me to the medical papers, and he said to google it (specifically "donor supply" and not "FUE donor supply")... I still can't find any papers that say anything that high.

When I asked, "What's the numerical difference between FUE and FUT? I've heard FUE gets half of FUT, but I've also heard 5-10% difference." he said "10%, and might be half depending on who pulls the grafts. There's three tiers of FUE. The highest quality and best result is manual, there's only 10% of us that are true FUE specialists, we are the best. In the second tier, 90% of the guys can't do FUE so they buy the machine. The quality of grafts isn't even close. In the third tier, Smart Graft and NeoGraft, it's 100% done by technicians. On average, for FUE, it's 80-85% growth rate, it can go down to 75, it just depends on some people and how their body is. For strip method, its 90-98%. So on average, it's 10% difference."

Should I believe his 8,000 number? Perhaps he's just better able to harvest the donor area, so he can pull out 8000 where others can only pull out e.g. 6000?

Or, since I can't find anything online that reflects his 8000 number, should I assume as low as 4500? If it's that low, then I probably shouldn't proceed with the 500...

Your thoughts and advice would be greatly appreciated! It's stressful wondering whether I can trust my surgeon, so some insight and knowledge would make me feel a lot better. Thanks in advance!