@Vincent Berg
Often, in these cases, the information will be in a Bibliography or Footnote page, rather than on the Copyright page, just to leave room for the official copyright notice.
I've found I've room to put it on the copyright page, and have done so. Take my Clan Amir series of 45 stories as the most affected. The stories Heritage, Fighting Birth, The Dareed War, The Darmore Demon were all written between 2001 and 2007, as was most of the stories in the series. I then published them all in a book titled A Fighting Heritage in 2007 with that copyright date as I didn't keep a track of the original dates until 2007. I then did an omnibus collection of the stories in A Fighting Heritage, The Shukra War, and the U MAMA War in 2011 as The Berant U Mama Wars with the following:
This is an omnibus compilation of the previously released books
listed below, they're listed and printed in chronological order of the
events in them. They follow the major military conflicts of the country
of Berant and its royal family as they fight a foreign business group
known as U MAMA. The major attack detailed in The Day of Blood is
not included here as it's in the omnibus The Falcon, which follows the
growth and development of Gerry Mannheim. The events in The Falcon
occur between A Fighting Heritage and The Shukra Wars.
To make the compilation easier to read, some sections of duplicated
background material have been delete and some have been amended
without loss of information.
A Fighting Heritage
The Shukra War
The U MAMA War
Copyright Β© 2007, 2008, and 2011 by Ernest Edwards
All rights reserved, including the right to reproduce this book or
portions thereof in any form.
At that time I had what was originally 7 books in 2 omnibus collections. In 2017 I collected all of the stories into one anthology titled Clan Amir of Berant and the current version has the following copyright page message:
This is a compilation of the books below in the chronological order of the events in them. They follow the problems of a country fighting for it's independence, plus the key parts in the lives of their warrior leaders and the lives of the country's people. Some sections of duplicated background material have been deleted or amended without the loss of content to make for easier reading, but some of the duplicated material hasn't been removed due to how the original books were written and it was felt the changes would detract from the story the material is in.
About Berant
A Fighting Heritage
Falcon Chick
Falcon Fledgling
The Day of Blood
The Falcon in Flight
The Shukra War
The U MAMA War
As well as the book titles above they have also been previously published as the two anthologies:
The Falcon
The Berant - U MAMA Wars
______________________________________
Clan Amir of Berant
Copyright Β© 2007 - 2019 by Ernest Bywater as Ernest Edwards
This shows the original and current copyright dates and the publication history.
I've found the copyright page to be big enough of handle all of that information OK.