The project didn't come back to me until about a week ago. When I restored the heads to their bodies and got ready to glue back in the cover for the opening at the back of the heads, I got a shock - the pieces will no longer fit into the holes they came from!
What has happened to these "open" doll heads in the 3-4 months that they sat around without the "cover" glued into the head/sphere opening is that the opening has stopped being the shape of a circle and is now more like the "prolate ellipse" shape in the drawing to the right.
All I can think of is that there must be pressures on the surface of the vinyl "sphere" of a doll head that cause it to gradually change shape if part of the "sphere" is removed. Apparently the shape that the head "wants" to be is longer and narrower.
So ..... learn from my mistake!!! Beware of opening up a vinyl doll head and leaving it open for too long!!! R.