It is currently not possible to run a single node network, then add nodes later with an upgrade. The event validator does a special check for single node networks that allows the other parent to be the same as the self parent. We create such events because of a consensus quirk with single node networks. The reason the network cannot be grown to more than 1 node is because this check does not evaluate the correct roster when determining if the event was created with a size 1 roster.

The best solution is to create single network events properly - with no other parent - and add the other parent in the Consensus Engine right before adding it to the consensus algorithm. When the consensus algorithm is enhanced to not need this extra step, it can be removed. Meanwhile, the events will be created and validated properly.