Let say I wanna download www.abc.com/abc/ and all its child nodes

I put -* +www.abc.com/abc/* in scan rules, everthing success in the end

I have all files in www.abc.com/abc and all its child nodes downloaded. 
for example:
www.abc.com/abc/123/
www.abc.com/abc/456/
www.abc.com/abc/789/

About 1 week later I tried to update just one of the child node let say
www.abc.com/abc/456/
so I changed the scan rules to -* +www.abc.com/abc/456/*,
in the end, winhttrack erased all others already downloaded except the
456?!!!
I once thought the scan rules is just the filter for downloading websites but
I was wrong!!! I have to redownload everything once again........
what should I do to avoid winhttrack to erase downloaded files when
updating???