Thanks for your thoughtful comments, ILTTATT. And I agree that what I say about the evidence for the cross can also be extended to anything that is not explicit in the Gospels. For example, we really have no idea what Jesus looked like apart from very general impressions. Whether the Gospels themselves are reliable is subject to debate but they are the earliest record we have regarding the life of Jesus.
I find slim's comment regarding the provenance of the earliest mss quite relevant (as usual). How much more likely it is for mss that were written in Egypt to make use of the Ankh as a nominum sacrum when they were already accustomed to its significance as reflecting eternal life.
I am certain that the editors of the NWT are well aware of the nomina sacra. In the 1984 revised edition of the NWT it includes P 45 , P 66 and P 75 in the footnotes and the use of the nomina sacra in the NT is one of the arguments that 'Jehovah' was replaced by 'Lord' or 'God'. As George Howard wrote in his article on 'The Tetragram and the New Testament' (JBL, 1977, pp.63-83) :
...conservative Jewish Christians probably continued to write the Tetragram in their copies of the LXX. Toward the end of the first century Gentile Christians, lacking a motive for retaining the Hebrew name for God, substituted the words kurios and theos (kurios being used more often than theos) for the Tetragram. Both were written in abbreviated form in a conscious effort to preserve the sacral nature of the divine name. Soon the original significance of the abbreviated surrogates was lost, however, and many other contracted words were added to the list.
As for Nazareth, if I may put my oar in, I visited some years ago and stayed at the Sisters of Nazareth convent. I'm not sure if that was JW-approved but thought Paul would allow it as "making use of the world". Anyway, while I was there they kindly showed me some excavations going on which were of a first century house they maintained was probably that of Joseph and Mary. Whether or not that was wishful thinking I notice an article in the Antiquaries Journal, Vol.92, pp.37-64, September 2012 which refers to :
...the archaeological site at the Sisters of Nazareth convent in central Nazareth [which] has remained unpublished and largely unknown to scholarship. However, work by the Nazareth Archaeological Project in 2006–10 showed that this site offers a full and important stratified sequence from ancient Nazareth, including well-preserved Early Roman-period and later features. These include a partially rock-cut structure, here re-evaluated and interpreted on the basis of both earlier and newly recorded data as a first-century ad domestic building – perhaps a ‘courtyard house’ – the first surface-built domestic structure of this date from Nazareth to be published, and the best preserved. The site was subsequently used in the Roman period for burial, suggesting settlement contraction or settlement shift.