I run an integrity check on the data every so often and just did one about half an hour ago.
Quite a surprise to find over 300 flights missing! Don't know what happened to it all.

Very occasionally one may go missing, but never that many.
Anyway, I've been able to import them all from FSA again.
The integrity checker compares the total number of flights, total miles and total hours between the CBFS database and FSA since May 2006. So I can be 100% sure they are all present and correct again now.
DM