"show that, unfortunately, it is also possible with dilligent rolling not to have any effects after 2 months, not even new vellus" < Rolling itself won't help much. Minoxidil is as important as rolling in the two studies.
Take some time to read both studies. It helps a lot to understand how you can replicate the method and what is really happening:
ncbi.nlm.nih.gov/pmc/articles/PMC3746236/
docdroid.net/Q4cnC2V/101080-at-1476417220171376094.pdf#page=13
You are not doing it like they did in the studies and that's maybe why you can't see early results like many others on here (and outside this website). Wounding alone or Minoxidil alone don't give much results (you will have to wait a lot more with wounding alone or rapidly lose a lot of new hair with minoxidil alone). It's the combination of both treatments that seems to work well (for whatever reason; it remains to be explained). The problem is that you are using Minoxidil only once a day. If you use minoxidil only once a day, then you should expect lower results or/and you will have to wait longer (that's my understanding).
What they did in the studies:
Lenght of the needles: 1.5mm or 2mm (Indian study: once a week at the beginning, then every two week / Chinese study: every two week) / Minoxidil: 1ml, twice a day.
For the Indian study they used a dermaroller and for the Chinese study they used a dermapen.
First little results were seen after 6 weeks (Quote from the Indian study: "Initiation of new hair growth was noticeable by around 6 weeks in Microneedling group and by 10 weeks in Minoxidil group."). You are at week 8. Only 9 sessions in, with minoxidil once a day. Your case sounds very normal.
You have to be more patient if you only use Minoxidil once a day. Also, if you can (some people can't, so it's up to you to decide), use Minoxidil twice a day. Then, maybe, your head will show vellus and hair more rapidly.
With what you are doing, you can't compare your very own case with the others, I think.