When I checked the installer held slimjet 4.0.14.0 using 7-Zip (unpack installer and portable version) is a file there "peperflashplayer.dll" and "\PepperFlash\manifest.json" it was said, there is an old version.
According to the changelog should be higher, and the option to slimjet://components allow for future updates plugin Flash better than in Chrome:
4.0.14.0
• Make flash player updatable as an component (Visit chrome://components)
• Updated flash player to 18.0.0.209 <------ this point


EDIT:
I Suppose merge floders "slimjet\PepperFlash" and "Slimjet\User Data\PepperFlash\XX.0.0.XXX".
You should then go to avoid new unnecessary directories.
XX / XXX - number version Flash.