Well, I never did get DTTG 1.5.3 running on my iPad3. Maybe the iOS version was too old at 5.1 but for other reasons, I could not upgrade it.
However, I was able to export the data, using the Send to iTunes option in DTTG Troubleshooting Settings. Good.
I have given up with the iPad3 and bought a new iPad Mini running iOS 8.1.
I am pleased to say that DTTG 1.5.3 installed on this with only very minor hiccups. Sync’d with DTP 2.8.1 and am able read most RTFs and edit some of them. Good enough. Will not use RTFD format on these DTTG sync’d files.
Did not have to resort to using the iMazing.com app - but that looks like a promising tool for future if I get stuck again.