There is no upper limit on the number of networks that you can monitor with one Asset Discovery node. This applies both to the production version and the evaluation version.
Asset Discovery allows you to use all network adapters installed in the host computer to discover and monitor local networks. In addition, you can use routing to discover and monitor remote networks. On top of that, CIP Route Browsing can be used to discover and monitor even more networks that are "hidden" behind Ethernet/IP devices.