Instant Mytol longevity

It's been a little over a month since I mixed some Instant Mytol and used 500ml of the developer stock. I put the used developer in an 800ml bottle with no attempt to evacuate the air and as a test to determine how much activity was left, tonight I did a snip test on the leader of a roll of HP5, which showed that the developer was still active. I just developed a roll of 35mm film with the abused developer and the resultant negatives were perfect. I guess I can put to rest any worries of the sudden death syndrome regarding mixing the developer with my well water and my opinion of this developer has not changed. If you decide to try the developer, I would, of course, suggest that you mix it with distilled water and form your own opinion. As for me I think I've found my new favorite brew and I couldn't be happier.
Denise Libby