The developers of AC created a unique time system. However, the in-game calendar is incorrect. First, the date given varies by server. At the time of this edit (July 24th 2010) the following dates were displayed on each server:
- FF: Morningthaw 24, 132 P.Y.
- HG: Frostfell 29, 131 P.Y.
- LC: Morningthaw 2, 163 P.Y.
- MT: Wintersebb 4, 180 P.Y.
- SC: Wintersebb 30, 124 P.Y.
- TD: Leafdawning 29, 133 P.Y.
- VT: Thistledown 6, 79 P.Y.
- WE: Snowreap 6, 117 P.Y.
- DT: Leafcull 11, 131 P.Y.
Since the dates vary by server it cannot be used as a reliable measurement.
Second, the dates on the calendar progresses at a faster rate that dates given in lore. In game, a full day-night cycle lasts a matter of hours. The rest of the in-game calendar is based around this. However, in lore terms one year in the real world and one year in Dereth are equal. For example, in Dereth there are only four seasons per real world year instead of per in-game calendar year. And most importantly, whenever the PY is referenced in lore, it is written in the correct year (For example 1999 = PY 10, 2009 = PY 20).
Conclusion
The in-game calendar is not correct. It is likely that the calendar panel has not been corrected since it is a minor issue, and fixing it would could potentially interfere with the day/night system. For the correct Portal Years and Roulean months as they correspond to the patches and real world dates, see Patches.