The license should prevent you from exceeding 2000 elements with a warning message.
You can keep adding nodes but other items will not get polled.
Actually, if you have an SL2000 license with 820 nodes, 1140 interfaces, and 40 volumes, you have not yet reached your license limit. Orion is licensed based on the highest of those 3 numbers. So, until you reach 2000 interfaces, you are still within the limits of your license.
Ok, so, is there some feature that show the amount of free license status?