Hmm, haven't heard of this one before. There isn't any chance that you might have accidentally deleted / reinstalled your copy of Pleco in the course of upgrading to the latest version, is there? (did you upgrade on-device or from iTunes?) And this is the Searches, not the Entries tab of history, right? Can you give me a rough idea of what you've done with Pleco (amount of use time, modules / features you've used, etc) between the last time you remember seeing your history fully intact and the first time you realized there were searches missing?
As for the reviews, I think Apple may apply some sort of screening to some of them but I'm not sure why it would take this long to post - are you sure you're not checking the wrong store's reviews? Reviews only show up in one country's iTunes store, generally - we have a program that pulls reviews from every iTunes store, so if you let me know what username you used on your review I can check and tell you whether or not it's posted (and in which store, so that you can then open up that store in iTunes).