Assignment rules. There's a difference in the rules for assignments made before 1978 and after (it gets particularly complicated if it's pre-1978). These laws were intended to provide a means for copyright owners to terminate bad deals made years earlier. We're not clear how a judge would rule regarding the potential assignment reversion but based upon your facts, it seems contrary to the spirit of the law.
The settlement. If a dispute does arise over an attempted rights reversion, the answers to your questions will likely come from a review of your settlement agreement -- that is, a judge or arbitrator may look to the settlement for guidance. If you can afford the fees, you could take a pre-emptive step and have the settlement agreement reviewed by an attorney.
The new serial. It's difficult to see what rights the publisher could claim to your new series. Perhaps the editor could argue it's a derivative work and therefore the editor has rights on that basis. We think that's a difficult claim to pursue (given the facts presented here).
Wildcard dept. There are also a couple of wildcards. Apparently you're talking about a serialized work and it's not clear what elements of the serial are covered by your agreement and which ones are not -- that is, we assumed you continued to create new serial contributions after the settlement. It's also not clear who acquired trademark rights in the settlement. In summary, your situation may be too complicated to rely on the generalized analysis of the Dear Rich Staff; if this situation is creating anxiety, pick up the phone and call an attorney versed in copyright law.