On the Adobe Forum, I asked: If I let my retail LR5 access my LR4 Catalog, will it retain the develop history states from the left-hand pane? I often want to return to an image and undo a few of the latest adjustments but not all, so it will be a disaster if the history isn't transferred to the converted catalog. A very quick reply from an experienced user assured me all would be well. It wasn't. As you can, an extensive history of adjustments has vanished. I can revert to the original raw state but not step back in a linear fashion to undo the last five adjustments for example. I'm pretty sure this is because the record of adjustments isn't in the catalog which is just a library, but in a sidecar file or xmp file. But All I did was ask LR5 to import my LR4 catalog. Should I have used a different method? Maybe create a new catalog then import all my folders and images???
OK panic over, opening my old catalog and letting LR5 convert it has worked. To remind others why it went wrong, after I installed LR5 and firs ran it it immediately offered to import my LR4 catalog. So I assumed this is what I should do. But wrong. I should have pointed it to my old catalog and let it convert, not import.
Brian, if maintaining your adjustments is so vital to your workflow, you might want to go into Lightroom preferences and have it save adjustments to the XMP file rather than to the catalogue. Doing this will slow Lightroom down very slightly, but the advantage is that if your catalogue is ever corrupted or lost, you will always have the adjustments in the xml sidecar file.
This kind of thing is another reason for the importance of backups. An incremental backup system, which can save multiple revisions of files, is very helpful if your editing software's own database gets corrupted.