@endsormeans at the beginning I was using PR 1.1.1 and wanted to upgrade to PR 1.3 Now I was just curious to know why I cannot see an update. It is always interesting to know why something is not working even if there are workarounds.
My phone was not new so it made sense to flash the device but upgrading to PR 1.3 without flashing would be useful for someone who managed to buy a new N900 or someone who did not use his N900 for several years and does not want to mess restoring his device configuration and data.