Cheers Jon,
No, I'd un-installed it from my development device, then installed the version from Google Play Store (the older version) allowed 'automatic updating' then I uploaded the new apk with some latest changes notes etc.
I noted that Google Play states that it might be some hours before changes take effect but I was hoping I'd see that familiar little downloady icon and be informed that BTInterface Free Trial BETA had been updated with ideally a screen showing me the latest changes notes but nada.
I could see that the new version was there from my PC. So just now I uninstalled it again and installed it from GPS (Google Play Store) and its the new version.
I was wondering if there was some setting or other on GPS that I'd not done or if it was because I'd changed the category from 'tools' to 'education'
its a mystery