Forgive me if I misunderstand... but testing two rolls is not much of a test.
Originally Posted by Alessandro Serrao
There are SO MANY variables. When you see underdeveloped negatives it just means... you need to develop them longer. Product failure is usually about the last culprit. Temperature / forgetting to shake the bottle / a mistake or two in mixing / not testing for your own times / too gentle or infrequent agitation (I could go on) are all more likely culprits than product failure at this point.
I'm currently dabbling in D23 but I have been using Rodinal / Adonal (whatever it is called now) for several years and never had a bad batch. I've certainly made mistakes during that time and produced bad negatives though.