I am not in a position to post links to your standings guides (my phone is being cranky with copy/paste), so tagging each of you to provide relevant info, if you so desire, on R&D agents, corp vs faction standings, and pros/cons of storyline missions in this context.
@Zhalyd_Lyehin is correct. If you want to get Storyline offers from Duvolle Laboratories, you’ll have to make sure one of their Storyline Agents is the closest one located nearest to the regular mission Agent that you complete the 16th mission for.
For more info on how to repair negative standings or to boost positive standings, check out ‘The Plan’.
When I was doing the same thing for the same reason several years ago, I found Brens Devalon in Scuelazyns the best agent to do business with. Storyline agent is next door and I don’t recall any lowsec missions.