OS X 10.9.5 Time Machine backups missing files (Mavericks)

I'm currently running OS X 10.9.5 on my 2012 Mac Mini.  Based on all the trouble reports I've seen online, it'll take me at least one more release before I consider going to Yosemite (OS X 10.10.x).

Anyway, a couple days ago I was editing some old photos stored in my user/Pictures folder with a third party utility.  I messed one up and to make matters worse ended up saving it over the original.

No problem I thought - I use Time Machine (and have for several years) - so I'll just open it up and restore the original photo.

Imagine my surprise when I opened the most recent TM backup and there were only 40 objects in my Pictures folder. There should have been 337 - and the photo I wanted wasn't one of the forty.
 
I started going back in time and had to go all the way back to Oct 14th 2014 where the Pictures folder had over 300 objects in it. The TM backup from Oct 21st 2014 only had 30 objects. Skimming forward in time from Oct 2014 the present, the backups of my Pictures folder contain anywhere between 30 and 40 items.
 
I have no idea what happened, (maybe I upgraded from 10.9.4 to 10.9.5 in mid-Oct???), and more importantly, no idea how to get TM to start backing up all my Pictures again.

I then checked a few other folders at random - like my Documents - to see if they're being backed up properly. From what I saw, all the other folders I checked looked OK.  

Sheesh....I've never had issues with TM in all the years I've been using it until this.  I've even done full machine machine restores from TM backups in the past with no problems.  Needless to say, it shook my confidence that I can easily restore a file if need be in the future.  Plus, I still wanted to fix my Pictures folder backups from here on out so I can restore them if I have to.

Searching on the web showed I'm not alone - people have been complaining of missing files in their TM backups for a couple years at least (and not just from their Pictures folder either).

Anyway, out of the several "solutions" people offered, here's the one I tried that worked.

I went into my TM settings and excluded my Pictures folder from being backed up the next time TM ran.  After TM completed its backup, I then went in and took my Pictures folder out of the  exclusion list so it would be backed up the next time.

After TM ran again I went into Time Machine to check the folder and YES - all 337 objects were backed up!  So far it's been 4 days and my Pictures folder has been backed up properly every time.  I'll call it case closed for now, but will have to keep a closer eye and inspect my TM backups now and again, and not just "set it and forget it" like I had been.