How does TM identify a changed file?

Size? Modified date? Checksum?

I have found that TrueCrypt volumes remain unchanged as far as Size and Modified Date, regardless of activity in which data is added or changed within the mounted volume. If so, is TM skipping this file after its first backup on subsequent backups?

 

Modified date. It backs up all files changed since last backup. Anything else would be difficult since all files would need to be compared. Calculating a checksum for all possible files would take a long time.

There are some details here:
Apple File System Events

Truecrypt not updating the timestamp surely has some security reason. But you can enable it in Preferences. On the Security tab, there's a checkbox for "Preserve modification time of file containers". When unchecked, this will update the timestamp of the TrueCrypt container whenever its contents change.

 

Thanks, Wave.
That's what I was looking for.

So, TM has probably been overlooking this file on each incremental backup. Since I rely on my encrypted files, it would have been a shame if the worst were to happen, and then only find out TM never backed up the changes this whole time.

p.s.
Tried to add a Rep to ya, but NBR says that I have to "spread it around" before I give it to you again. You have always been more than helpful.