1. Do the sites get into other SEs?
2. What's your process for getting the initial listing in G?
If Q1 gets a yes, then Q2 is the key; if you are using any kind of 'personal link network' - however small, then check it has not become contaminated by a bad neighborhood; check your older sites.
I use my existing sites to promote my new ones, and have no worries (I'd do the same with bricks and mortar), and I don't think Google worries either.
But I do it sparingly, and remove the links once the site is free-standing and independent, with its own directory entries and links.
Why, if it's so 'OK'? Because if your sites are heavily interlinked, the one bad apple syndrome applies; if one reciprocal, on any one of your sites has 'gone bad', every single one of your sites is at risk, even if you have done nothing wrong - and newer sites are always first to show problems.
All this may, of course, not apply in the least - but worth thinking about with your kind of problem.