Version Control

What stage is this?
Didn't I leave a bookmark in this library?
I suppose it's sticking out the top
And all I can see is the spine
Titles don't reveal whether 
You're being read
Or even understood
Where were we?
One point oh was a lifetime ago
How many lifetimes are there?
The numbers should tell me
But they've all gone home
Each chapter has a phrase
Could it be alphabetical?
No chance; that was twenty six years ago
At seven in the morning, when it started
We each made changes
And lost the threads