Multiple examples of photos jumping to other Events, disappearing completely, and jumping to iPad out of iPhoto

Question

     I had almost 1000 rendom photos jump into iPad and OUT OF iPhoto six months ago.  After numerous one-to-one helpers, one person was able to extricate them into a file in "Pictures" on my MacBook Pro.  (First, I had to go through every photo and match with iPhoto to see which ones were missing!  Hours of work.)  They still remain in a file in Pictures, but the event in iPhoto that I made for them worked for awhile but now is transformed into a file of a different event with its pictures repeated about a dozen times. 
     I tried to create an album today out of a specific event and several of the pictures disappeared in the process, both in the Event and in the Album.  A bit later, the Album is empty and the Event contains the reduced number along with some other pictures from an unrelated Event.  I also have a couple of folders that show only a grey image of a palm tree as the cover picture and it says there are zero pictures, but in fact there are pictures inside.  Choosing a different Key Photo doesnt' work.  Merging some with another Event did not work and the pictures disappeared. 
     In the meantime, the number of photos that is shown has changed and it tells me that there are 16 photos hidden - where??
     I do have a very large number of photos (28,000) ... too many?  My machine is four years old with expanded memory and storage.
     Any ideas? 

Answer 1

1. 
I know - it's impossible but it happened.  Of probably 5or 6 different people at Apple, including Genius bar folks, no one had an answer 
2.
It's 9.4.3 iPhoto 11 
3.
I moved the 33 pictures in my EVENT into the new ALBUM.  From the ALBUM I proceeded to select the ones I wanted and "remove from album" the ones I didn't want.  (This is a process I have followed many times to get the pictures I wanted for albums on my website.  I upload from the album.)  This process was not complete when I discovered the problem of lost pictures that I can find nowhere.  Eleven of them are gone from the original EVENT (replaced by pictures from a completely unrelated EVENT) and the ALBUM is now empty.
4.
Yes, EVENTS is what I meant.  This problem is not understandable and is a puzzle for the person I most recently talked to at Apple store.  She suggested that I copy the pictures and then make another EVENT.  As an alternative, I didn't copy them first, but then I "merged" them with the EVENT where they belonged - it didn't work and they were lost. 
5. 
I have checked this option - however I see no change.  Where should I be looking for the photos???  Maybe I don't know where to look. 
6. 
Well, at least that's good news!  Thank you! 
Thank you much for taking the time to consider my questions.  I have spent a great deal of time and energy with my photos, learning at the Apple store employees over 4 years, primarily with 1 to 1 seesion about all the details, and am very familiar with iPhoto.  But with the latest problems, I am baffled.  I thank anyone who can help