I confirm that it works (RPI3 + recalbox 4)
Using windows 10, edit with notepad++ config file: \\recalbox\share\system\configs\retroarch\retroarchcustom.cfg
Adding a new line (just under the line : video_aspect_ratio_auto = true )
video_crop_overscan = false
Castlevania screen is complete, you will see the S P and E at the upper right side.
et Voila ! 😄