[u][b]Canon and Non-Canon[/b][/u]

Canon and Non-Canon (please observe the spellings; 'cannon' is something else altogether, and 'headcannon' even more so) are terms that have a difficult definition when it comes to running RP's in a shared setting. 
Overall, 'Canon' starts with what is outlined in this guide, and in Shattered Steel and Armoured Fist, as they are the first two RP's run in the setting, and are run by the writer and creator of the setting itself, and the Guide defines the canon. 

As a rule of thumb, if any other RP adds outlandish or unusual elements to the setting - for example, an RP that was concerned with Magic within the Heavenfall setting, or hunting supernatural creatures, or an alien invasion - then it would be non-canon, as it would be a [i]vast[/i] change to the established tone and rules of the setting, and such an introduction of an element would be a sweeping change in everything that is understood in the world of the setting itself. 
Likewise, any RP set in the future of the setting would be considered non-canon, as events have yet to be defined and shaped by the ongoing RP's within the setting, so by definition, any future-set Heavenfall RP's would be making up their own history from the 'present' 2014 of the setting. 

To run a Canon RP within the setting, it would have to avoid affecting global events on a wide scale, or be very carefully run to incorporate ongoing events in other RP's, or at least pay passing mention to them, and vice versa with the ongoing RP's. There is openness to this, to a degree, as long as - as previously stated - it does not have any massive implications for ongoing RP's and their plots, characters, or other aspects.