Keep in mind – the LB Sudoku Generator licensing accounted per copy of InDesign. Sadly enough, that means that if you have two copies of InDesign installed on a single machine (e.g. CS3 and CS4), which need both to be licensed, you’ll also need to purchase two licenses.
There are no provisions for upgrading or side-grading – the cost of a single license is kept purposefully low, and does not reflect the real cost nor the real value of the plug-in. Instead the fee is a contribution towards further development.
To allow us to sustain the low license fee, we decided not to allow for the administrative overheads involved in tracking things like upgrades. Instead we use a very simple, automated system and we charge a fee per installed copy of InDesign.