One thing to keep in mind is that the screenshots names are based on which date it is of the year. Some typical names listed below since this could be your issue, also good if everyone knows this since I've even told some staffers this when they didn't find their screens.
screenshot_03162015_051617336
That means the screenshot was taken 16th of March 2015(Bigger text is highlighted)
screenshot_02032012_070417645
That means the screenshot was taken 3rd of February 2012(Bigger text is highlighted)
But even though the second one was taken 3 years ago, it would end up before in the folder when files are listed by name.
Since windows file manager, or in general most are set to order files by their names a-z and numbers 0-9 so will the screenshots and their names. I personally make folders for every year on FeralHeart and cut and then paste the screenshots in there, that way screenshots from the year before will not get mixed up with the rest more recent ones. What must be understood is that due to how the game names these files, as soon as we start a new year, the game will place the files in the beginning of the list again, even though the screenshots are newer due to how the files are named when they are made.
A simple way to find a recent screenshot though would be to change your file view to a list by clicking the "change your view" icon, then just click the date tab since it would make a list from most recent made file instead of just based on name. Or just make a habit of what has been mentioned above and make folders for every year and keep the main screenshot folder for current year only.
If you believe however this is not the case, then it must've been that you didn't take the screenshots or they've been moved or deleted by your or someone else.