Stupid Question: Does access to Partner Center require additional full license?

OK, call me naive, but thought Partner Center access was license free, similar to Customer Center. Seems when I went to add access for a Partner I received a message stating I exceeded licenses.

We paid for an "Advanced Partner Center module" which if we need to *additionally* purchase licenses for seems not a useful option for us.

Is this true? Do we need to pay for the full license (ERP and modules total)? that seems a bit excessive for giving partners access to only a subset (e.g. solutions, cases for example).

NetSuite, please let me know on this since I can not find ANY documentation (including sales licenses, order, etc) that states this. If true I suspect this will p**s a number of execs off since I told them differently when we purchased this.