Of course you are worried. Lymph nodes can and sometimes do hold cancer cells in a contained environment for a long time. The problem is Doctors don't know and we don't have reliable means to detect circulating cancer cells-for all cancers- in the blood stream yet..You just pray that the Lymph was doing its job and held all cells in its self.
There are several clinical trials working on detecting cancer cells in the blood for many solid tumors as we speak.
Chemo kills circulating cells. For some people the chemo gets them all for others it may not. Chemo has a harder time killing solid cancer tumors, but even then some solid tumors are killed with chemo, and their are a number of reasons for that..all of which are in clinical trials somewhere trying to break the beasts back. Trying to get Chemo drugs to get inside the tumor and kill it.
For Lung cancer, many experts think its better to remove as many Lymph in the center of the chest as possible because these nodes can harbor undetected cancer cells that can come alive later and spread. so I see the removal of more than one as a good thing.
Sometimes radiation is given to a tumor and sometimes it is given to a place that has had a surgical removal of a tumor because Docotors now know that the environment around a tumor may have a signal in its DNA to start some more cancer growing. So in certain instances radiation to the area can help reduce the cance of cancers return.