What does the 'Operational node count' mean?
It means how many nodes are active, estimated ROI is based on the number of active nodes:
60% ROI per year @ 250 Masternodes (3 month projection).
30% ROI per year @ 500 Masternodes (6 month projection).
15% ROI per year @ 1000 Masternodes (1 year projection).
3.8% inflation year 1, block reward decay by 5% per year, reward target schedule 40 years.
projection was made by the dev team.