Hi
Welcome to the Microsoft community.
I understand that you are suffering from the problem of "windows explorer search partial results." If my understanding is wrong, please feel free to reply and correct me.
Your failure to search for files with the A initials may be due to a problem with the system index. You could try to rebuild the system index and directory location. Follow the steps below:
1. Open the control panel by typing Control panel in the search box at the bottom left corner of the desktop . 2. Change the display of the Control Panel to a small icon display and click on the Index option.
3. Click on Modify - check the folder and path to create the search - click on OK.
4. Click Advanced - in the Index settings tab and click Rebuild.
After clicking Rebuild, Windows 10 will make the following message: Rebuilding the index may take a long time to complete. Some views and search results may not be complete until the rebuild is complete.
Click OK to confirm the rebuild of the index.
If the above does not work, you can also try use a command prompt to open the troubleshooter.Check this link for more help.
Press Windows logo key+R, enter cmd in the Open box, and then select OK. At the command prompt, run the following command:
msdt.exe -ep WindowsHelp id SearchDiagnostic
You can also try using the System Restore option to try to restore the system to a normal time period and see if that helps.
You are welcome to reply to this topic at any time, let us know if it helps. ^.^
Best regards
Derrick Qian | Microsoft Community Support Specialist
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* Please check and vote this answer if it helps as it will be beneficial to more community members reading here.