On my way to removing dark and deep ink

Clearly the ones on the hand are the most resistant to come off. Between the first and second session 60 days, third after another 5 months and fourth after 1 year . The last session was 3 weeks ago, so the skin is already "healed". I got wounds in some darkest areas this time, it had never happened before. The last tech said there are about 6 sessions to go. The oldest tattoo is 5/6 years old