I have noticed that at some zoom levels, the latest work done is not rendered. At higher zoom levels, the changes are seen.
See here, at Tala.
Upon zooming in further, you can see that some detailing has been added…
You can get information about the rendering process here : http://wiki.openstreetmap.org/wiki/Slippy_Map
If you want to know the date of last rendering, ask for example: a.tile.openstreetmap.org/12/2880/1836.png/status
If you look at a region and last rendering is older than 7 days, it is automatically entered in the rendering queue.
If you want a quicker rerendering : a.tile.openstreetmap.org/12/2880/1836.png/dirty
At high zoom levels, the map is rerendered online.