Divus,
I have had your post bookmarked and have been meaning to reply but other priorities called. Sorry no one has and sorry for this late one... At any rate I have had analogous issues - not quite the same as you but along those lines. I can explain my issue in more detail if you want but in a nutshell, I get what I call junk albums that are created automatically every single time my iPad Air updates to a new version of iOS 8. I keep one folder/album of my favorite travel pictures synced from my PC to my Air and "magically" right after any and all updates, my Photos App shows up with 4 to 5 additional Albums with the name of a folder I once had on my PC that no longer exists (at one time I had synced that folder to the pad also). These junk albums are populated with some of the same pictures from the one Travel album that had been previously synced (strange and confusing, I can post screen shots if interested). The Travel album is intact and the junk photos are duplicates. This issue has been at AppleCare Level 2 for 6 months who escalated it to Engineering, so far to no avail as they are at a loss (other priorities). For me this is not a big issue, all I have to do is re-sync my Travel album every time right after an iOS update and it wipes out the others. This adds about 5-10 minutes to the updating process.
At any rate, while researching the above and also how to sort the pictures so they show up on the pad in the order I want, I came across a pesky issue with iOS which may be of relevance to you. I sync from a PC but I also have a MBP and I can look at the same pictures there as well. iPads and iPhones (all iOS) display photos in the order of "date created" (using PC terminology) which is not necessarily the same as "date taken". All pictures start with the same taken and created date but as you copy, edit, etc. changes are made to the metadata and thus new created dates get established. For instance, copying (not moving) a picture on a PC preserves the date taken but established a new date created on the metadata (the new date being the date of the copy). On a PC, date taken remains fixed (unless I manually edit it). On a PC there is no way to edit the created date, maybe with 3rd party software, but neither File Manager nor Photoshop can do it directly (there is a workaround). My Mac however presents me with different info. For instance looking at my first picture on my Travel album on my PC I see the same date taken and date created 6/4/2014. Looking at the same picture (with no edits in between, simply copying by USB to Mac) the Mac shows "modified" 6/4/2014 (obviously the same as taken above) and "created" on November 29, 2014 which may well be the date that I copied the picture to the Mac.
The bottom line of this write-up is that I believe your issue lies with the metadata but not necessarily with the date created or modified that may show up on your Mac. This is the critical sentence here: I suspect that the pesky old pictures that keep showing up somehow while truly being old and showing the proper old taken date, may have been copied or somehow modified in such fashion that other components of the metadata present the pictures to your "Last Year Sync" as if they were actually taken last year. Does this make sense? If you had a PC I could elaborate further about making changes to the metadata. Since I have not done so on my Mac I cannot advise there. But I would start by going into Get Info in both Finder and your Photos App (Mac, not iOS) and see if you can discover some sort of pattern to the photos. If so I would be most interested in hearing about it....
Best,
elcpu
