Sitemap Generation doesn't seem to work correctly

[PiRaCy]

I'd been generating sitemaps without any problems up until recently, but since my host migrated my site to a new server things seem to be broken. But I'm not sure if it's a problem with the host, or whether it's my understanding of how sitemaps are generated that's the cause - extensive searching on the Internet hasn't enlightened me one way or the other, so I thought I'd ask here ...Prior to migration to a new server, whenever I generated a new site map, the resulting file listed ALL the pages on my site - every time, no problems. It's been that way since I started generating sitemaps 3 months ago - a new one every 10 days. The previously generated sitemap sat in the site's home folder while the new file was created, and the final result was always a complete map of the site, which I then uploaded to replace the old one, and linked to via Google WebMaster and Bing.But now when I generate a sitemap, the newly generated file seems to only be listing pages added since the last sitemap was created, whereas I still want a FULL listing.My robots.txt hasn't changed, and I use the same generator settings as I've always used. But whilst sitemap generators access the right folders OK, they aren't listing all the files in each folder.I've tried three different online generators, and even tried the PC-based GSiteCrawler as well, but the result is the same every time - all I see is the same subset of URLs from my site, instead of the full set.So my question is ... is this the way Sitemaps are meant to work - that they only collate pages added since the last map was generated ...? And if so, how do they tell which pages are new ...? And if not, what might cause a generator to fail to produce a full sitemap ...? Could it be something to do with the site being migrated to a new server ...?Thanks for any advice on this, I haven't been able to find anything through Google at all.