How old were the old tiles? :-) I admit, I haven't posted any updates since September. However, I just finished processing the December 16th snapshot of the OpenStreetMap database and will be posting that to my website tonight.
Your comment about old tiles getting flushed is unfortunately a design feature of the YAAC OSM preprocessing importer code. It replaces any 1x1-degree square tile with the new data for that tile in the input .pbf or .osm.bz2 file. So, if you are going to do partial segments of the world map, I recommend getting an export that is axis-aligned to whole degree boundaries (for example, -100 to -90 degrees longitude, +20 to +30 degrees latitude), rather than bounded to higgly-piggly political or geographical borders. It can't merge two files together because it is possible for a Way (polyline) to exit and reenter a 1-degree square tile, such that there are two Ways in the same .ways file with the same identifier (different pieces of the Way). The importer wouldn't know which ones of the old file versus the new file to keep (it is possible for OpenStreetMap editors to remove obsolete map features), so it just discards the old tile file entirely and replaces it with the new one for that tile based solely on the new input data.
This is why I routinely import the whole planet dataset in one giant lump. The last run took me not quite 22 hours to process (on a fairly high-powered gaming system), and will take another hour to compress the individual tile files for more efficient network transfer for other users.
Sorry about the bad news.
Andrew, KA2DDO
author of YAAC
