Yep, always concerned with voids on my boat. From every indication, sounding and moisture meters (never drilled there) there is no water intrustion. But there have been other WS's with some. The piece on the back of the full keel had some voids and filler in the glass work but when we refurbished her I ground them all out and filled and glassed. Any others ever found I filled.

Yeah, I'm not a Cat person and haven't studied them as you. But IMHO either fill the void or leave it empty. Seems half hearted the other way.

Ciao