Could you please check the below link as that might help you in organizing your catalogs:
Open the catalog that will contain everything, and then for each catalog file, you select File->Import from Another Catalog. Repeat until all your catalogs are now included in the one catalog that contains everything.
Thank you Sarika.
I have watched the video, but Julieanne avoids the scenario where the same photos appear in different catalogues, which is where I seem to be. I can create a master catalogue and import one of my existing catalogues in to it. If I then import a second catalogue which is older than the first and the same photo has edits in both, I was concerned that one set of edits would overwrite the other. As the "date modified" date of the .lrcat file reflects the date it was last opened, whether or not any edits were done, it wasn't possible to know which catalogue had the most recent edits.
I have just tested it and discovered that, if there is a duplication of photos with non-identical edits, there is a tickbox in the import dialogue box which creates a virtual copy. I think this solves my concerns.
Thank you for taking the time to advise me
Thank you DJ. Seems I can't highlight 2 replies as correct.