Slightly different way round - you could get more recent work into the backup catalogue....
In the current catalogue, select all the recently-edited images and do a Ctrl S (Win) or Cmd S (Mac). So we're saving most of your recent work back to the files (most omits virtual copies, stacks, pick flags.... but all adjustments and most metadata).
Now restore your backup catalogue and see if you can find a way to identify the above images. Are they all in a few folders, for instance. Then select them and do Metadata > Read Metadata from file. That should bring in your work and apply any edits to the published images too.
Editing the SQL could be time consuming and messy.
I thought about that, but I have been working all over my catalog, on virtual copies, flagging and stacking - all the things you mention won't copy! I'm not going to be able to remember which files I worked on, as it's been about 3 or 4 weeks since the backup, which is why I'm thinking of editing the database. I have opened the lrcat in SQL-manager (another copy - backupbackupbackup!) and can see the Photodeck plugin records, so thinking I could copy them...?
You can try, but there's no documentation in that area so you'd have to test carefully as you proceed.
What about this idea.... Restore the backup catalogue and do a File > Import from Catalog, importing into it the entire current catalogue. Publish service data is omitted from this method, though all the other non-xmp stuff should be OK.
Ah! That might work... I'll run the import and let you know. Thank you.
Actually, what I needed was the Publish data from the backup, and the latest edits from the latest catalog. I was going to import the entire new catalog into the backup version, but I found the "sort by Edit Time' feature, which saved me re-importing the entire catalog into the back. It worked like a charm! Thank you for your advice! Much appreciated! (One very happy LR fan here again!)