The change related to when a book was published only applies to older versions of the Kindle for PC/Mac app. Those apps can no longer access books published since the beginning of this year. No other apps or devices are affected by that change.
I do not know why you cannot locate the files on your device. Perhaps they are going to an alternate location on an SD card. But even if you find them you won't be able to use them. The Kindle for Android app downloads books in KFX format with DRM that is unbreakable so far. (Although it may be possible to do something if you install a very old version of that app. See the recent posts in the thread
Amazon and DRM changes.)