I have a chart that has many planets and points on cusps. The big three I am concerned with here are Pluto (zero Virgo), NN (29 Scorpio) and SN (29) Taurus. In the case of the NN and SN, the degree of the zodiac varies depending on which software I am using. They sometimes come up as NN 1 Sag and SN 1 Gemini. Am I correct in thinking that I should take both sets of signs into consideration when trying to interprete this? The same with Pluto. Should I blend Leo and Virgo together?
Most likely the discrepancy in node locations between software has to do with one using True nodes and the other Mean nodes. Mean is a mathematical smoothing of the actual movement of the nodes, which is retrograde 90% of the time and direct 10% of the time. In EA we use True nodes, because this is the actual movement of the nodes. Mean is a mathematical abstraction that never exists in the sky. Yet it is frequently used in conventional astrologies.
Usually there is a setting in these softwares where you can switch between true and mean. When practicing this form of EA we suggest setting it to True.
We never blend two signs together in the way you are asking about. 29 degrees is a culminating degree (although see my comment about the nodes below) and 0 degrees is what we call the beginning of a new phase. These are natural archetypes - endings and beginnings. It means cycles are ending and new ones beginning.
We use what is called the cycle of phases and aspects. If you have access to Jeffrey Wolf Green's book Pluto Vol 2, there is a long chapter in it that explains the meaning of all the phases, and the aspects within the phases, in the context of evolutionary cycles.
One thing to consider is the net motion of the lunar nodes is retrograde. This means having the nodes at 29 means they have just entered a new sign. Unlike all the other planets, this is a new beginning for the nodes. With all other planets it would be a culminating.