Hi Ted,
It's true that one can find enthousiastic reports of improvement after a few rolling sessions, but often that's because the mild swelling associated with rolling can give a better appearance. A few sessions over some months definitely is not enough to get results because the remodelling process takes months to finish. That means that only your first rolling session has "matured", and often a dozen sessions are required for significant results.
Especially for acne scars we sell our specially designed single needle, allowing you to treat them intensively and deeply from various angles, crushing the scar tissue. If you haven't tried that yet, you should definitely start. We sell them cheaply in batches of five. Also, you could consider rolling with longer needle length.
Not everyone gets good results with dermarolling acne scars though. There is a percentage of people who just have bad luck (it could be a skin-genetical issue). And some people get quicker results than others.
There are no long-term side effects because the epidermis is not thinned by dermarolling. So you can roll dozens of times over years and nothing will happen - except, usually, the beneficial effects associated with microneedling. It's the same with laser treatment and dermabrasion for acne scars - there also is a percentage of people for which it doesn't work.
It may be hard to stay focused and keep going even though you see no benefits, but remember that improvement in microneedling is exponential. You often only see some improvement after say half a year or even more than that. But then things accelerate. You can compare it with compound interest. Stay the course. It's only once a month at most. Keep doing it and report back a year from now. There is no easy cure for acne scars but dermarolling acne scars does usually give worthwhile results, with patient persistence.