As far as I understand, the producer is publishing to the 20 nearest nodes it finds, but the consumer is also searching the 20 nearest nodes it finds, and there is quite a big safety margin built into that number 20. Almost all consumers should still be able to find your object once it has only published to 10 or 15.

This is a probabilistic system anyway. Even if publication finishes to 20 nodes, why is that enough to return to the caller? Shouldn't it be 30, or 50, just in case?

I'd say it makes sense to return control once zero PUTs have been made and do the whole thing in the background, to avoid serializing operations that usually don't need to be serialized, such as publishing multiple objects.