Originally Posted by television2004:
“With regard to Teletext. I had a Philips N1500 VCR in 1974. The recordings clearly have Ceefax pages.”
Yes; as I said in my original post, they were already doing test transmissions in 1974. And I'm guessing you didn't actually have a Ceefax/teletext-compatible TV at that time!
Actually, on closer re-reading, the article says that they were doing tests as early as
1973, and that "the Ceefax system went live on 23 September 1974". So that's pretty early.
But it also says that "After technical negotiations, the two broadcasters
settled in 1976 on a single standard, different from both Ceefax and Oracle, which ultimately developed into World System Teletext". This implies that prior to 1976, the system wasn't unified and that early Ceefax was at least partly different to the later version(??)
BTW, you say that you have recordings from 1974 showing signs of encoded Telext.
This raises an interesting possibility... 
Received wisdom is that one needs S-VHS quality recording to retrieve stored teletext (VHS quality isn't good enough, I've tried it myself and you're lucky to get a few garbled characters).
However, I'd guess this assumes that one is only doing it via normal means (i.e. playing the recorded signal directly via RF to a standard television or computer teletext decoder). If it was possible to digitise and tidy up VHS, Beta or N1500 recordings- probably *not* in real time- it might be possible to reliably retrieve teletext signals from a significantly poorer-quality recording.
This of course is significant, because S-VHS only came along in 1987, and old tapes such as yours are possibly the only records of some early teletext pages. They'd definitely be of historical interest.
Just an interesting idea, and one I suspect others have also looked into...