I think all is explained. The track was originally generated and saved to PowerTracks when I had the megapack at the beginning of January. THat's the reference I've been using to try to regenerate the steel guitar. I liked BIAB 2018 so much I bought an upgrade to the ultrapack.

I checked the real tracks settings and there is an option to replace based on tempo. I think with the upgrade I got a whole lot of new RealTracks so now BIAB can substitute a RealTrack I didn't have before. So the steel guitar is actually different - 621 as opposed to 323 working from memory. Similar but different - hence the inability to get a steel guitar part reminiscent of the original.

It's a steep learning curve from the 2008 version!