It was around before the concept of subscription models existed...

It was around before the concept of subscription models existed from what I can see so perhaps back in 2000 when they got it they actually just bought the software outright and now only pay for development updates, meaning its really not a source of income given it’s a contract that they can simply not be paying ie. no development work

In general companies with bad balance sheets don’t hide income, not when the people hiding it are big shareholders themselves. It’s probably not mentioned since it’s too small to bother mentioning you will find