This is likely to be more diagnosis than recovery, I'm afraid.

First, if you haven't already, make sure you have copies of everything you can already see on the card, this process is destructive.

Next, use Photorec (freeware, cross-platform) to see if your newer pictures are potentially still there - my gut feeling is that they won't be, unfortunately.

Next comes the destructive test - this is to see if the card itself is still viable.
Do this even if you got your newer photos back using Photorec.

If an SD card has an error at write, then there is often firmware protection which will trigger to prevent further damage. The symptom is that the card becomes unwritable - sometimes it will appear to write, but the next time the card is ejected & re-inserted it seems to 'magically' go back to its previous state.
This is, to all intents & purposes, irreversible.

To test..

Try to format the card.
Try it three ways - first in the camera, then in the computer as a 'quick format' then again as a long format.
After each test format, attempt to write a file or two to it. From the camera, take a couple of quick photos; from the PC, drop a couple of small text files to it, etc.
Check each time that the new files are still visible after you eject & re-insert the card. Check the photos are also visible to the PC.

If all of these tests fail, you can be fairly certain the card is in write-protect mode & your only solution is to bin it & buy a new one.