after PR1.3 for OS2011, they could also start working on OS2013
not been Maemo user long enough (thus, before N900) to gauge in how far before the MeeGo / Harmattan release, which obviously meant a fundamental break from Maemo / Fremantle each release was the base for the following...

i think nearly each new version could be installed as a HE (Hacker Edition) on the previous device, so there must have been some compatibility which seems to be missing in Harmattan for N900