Excellent information so far, thanks very much. It makes sense that there are no actual "pins", just a hole for the nylon to be injected (I heard somewhere there are grooves on the shaft for the nylon to flow around?). So as mentioned, maybe the nylon is still in there and just the entry bit of plastic fell out.

But as mentioned the column is shortened per the photos. It appears about 2 inches too short to reach the proper coupler position.
I decided to take the column back out of the car since it was quick and easy, so it is in my garage. I measured the overall length of the shaft and it's 38 1/4 inches. I read somewhere the normal length is 40 3/4 inches so that would make sense
But the inner shaft does not seem to want to move at all! I had a quick go using a hose clamp on the bottom of the shaft and tapping with a hammer. It was on pretty tight but the clip slipped without the steering shaft lengthening. How tight should this be? It shouldn't be rusted in as I drove the car for years (at the correct length) then removed the column to rebuild it and it has been inside ever since.

Any thoughts as to my next move? I'd rather not disassemble the entire column again but I will if necessary.
Thanks again