What computer operating system? If you have not already, you should update 12 to 12.1 using an opened project's Help Menu/Updates.
But, to your immediate issue...
After you create a text title in the Titler and close the Titler, go to Expert workspace Project Assets, right click the thumbnail there for that title, and select Duplicate from the pop up menu. Then drag the Duplicate from there to the Timeline. Double click the Duplicate on the Timeline to open the Titler where you will edit the Duplicate. Repeat that for additional titles. Copy Paste is not the way to go on this. You saw the consequence of that with changing one text title changing all.
Please consider and then let us know if that worked for you.
Works perfect! Thanks for your help. That is a big time saver.
Thanks for the follow up with the great news of success. Great job.
Please never hesitate to ask if you have questions or need clarification on your Premiere Elements workflows.