Unable to correct dates in iPhoto 11

I have iPhoto 11 version 9.1.5. I know how to correct dates of photos and have done it successfully for years. Today, when I completed the process, the date was completely random and off by a few centuries. Looked online, but only found information on how to change the dates, which I already know.

I'm hesitant to update to a newer version for fear of something going wrong (date changes, album titles lost/disorganized, etc.) which has happened in the past. Thanks for any help you can offer.

So its obvious that you are running the latest OS or Mavericks, yes ??
Which tells me you are worried about updating and moving to Photos the new Photo App for OS X ?

All I can say, is do a backup via TimeMachine or with CCC or SuperDuper, and then update to 10.10.3. When this happens, if you have iPhoto in the Dock, this will be removed and replaced with the new Photos. iPhoto will still be on your System, so don't be worried about updating. iPhoto will be in the Applications Folder, so you can still keep using it.

Here are 2 links to get you started, the first by Chris Breen ~ Prepare your iPhoto Library for Photos and the second is by 9to5Mac How to move your if Library to Photos.
Between these 2 pages, you have all the info you need to update to the new Photos now, but like always, do a backup first, this way you can always go back to how it was, if anything goes wrong.