Lost my library I think-how do I know which one it is?

I have not been using my mac so I am a little rusty.

A few months ago I thought I imported my whole library into Photos.

Then when Christmas came around I hated the new look of building a book in Photos (family tradition at Christmas)

Anyhow I went back to iPhoto.

but I am only seeing 2 years of photos.

I also have upgraded my computer to a new hard drive probably 6 months ago so I do have several versions of my iPhoto library but am worried about combining and or overwriting. What is the best way to start ?

thanks for all of your help all.

Laura