Time Machine backup doesn't recognize recent changes 100%

I have an iMac and 2 external hard drives ("A" and "Time Machine" for purposes of this post).

I just updated my iMac and also A before running a manual Time Machine backup to "Time Machine".

What gets backed up via the Time Machine software to the physical hard drive "Time Machine" is my entire iMac and A. Nothing is excluded.

After the manual backup completed I opened my Time Machine hard drive icon and opened the folder "Latest" to review the new backup. I noticed a problem right away with the date/time stamps. When I open Latest I see 2 folders, A and iMac. The A folder is the problem in that I just put new files on A moments before I ran a manual backup however Time Machine is saying A hasn't been modified for the last month. The iMac folder date/time stamp however indicates that I just made changes to my iMac (which I did) pre-back up. And yes, I reviewed A to see that there are indeed new files there with today's date/time stamp info.

Thoughts?