Hi ciprian.ilie,
Thanks for contacting us with your question.
It's been roughly 6 years since 4.2.3 and it sounds like quite a big upgrade and it is hard to predict the outcome, because many things have changed since then and it solely depends on your chart config and number of custom changes. Whenever we can we try to keep backward backward compatibility, however some things surely changed for good. Nevertheless, anything that was created back then should be possible to recreate now without any issues. I don't know how complex your Highcharts code is, but If I can suggest anything, you should try to setup development environment based on latest Highcharts version and migrate one chart at a time, resolving possible issues.
Here is a Changelog where you can find an information about all changes:
-
https://www.highcharts.com/blog/changelog/
And of course in case of any concerns do not hesitate to ask.
When it comes to the licensing question, on this forum we provide mostly technical support and you should definitely contact our sales team. You can do it here:
https://shop.highcharts.com/contact
Let me know if you have any further questions.
Regards!