"I'm not sure of the impact this can have on the Wikidata-WikiTree connection. I'm a bit concerned by what it means for Wikidata data quality,"
To me it is bad news, if we are comparing what is on wiki-tree with what is on wikidata
I'm not sure I understand wikidata but if the data is incorrect, what is the purpose of wikidata?
I am familiar with the Peerage (mostly from barely sourced profiles)
The website uses a variety of sources, from the many editions of Burkes to emails from readers. http://www.thepeerage.com/s1.htm#s3268
I have to go by experience which of course may be exceptional but it leads me to worry about data on wiki-tree being compared to this data.
" Sir Nicholas Martyn was born in 1550.1 He married Margaret Wadham, daughter of John Wadham and Joan Tregarthen.1 He died in 1595.1
He lived at Athelhampton, Dorset, England.1
Margaret Wadham was born circa 1526.1 She was the daughter of John Wadham and Joan Tregarthen.1 She married John Young.1 She married Sir Nicholas Martyn.1 She died after 1606.1
Her married name became Martyn.1 Her married name became Young.1 "
Even a brief glance at the respective birth dates of Sir Nicholas Martyn and Margaret Wadham should signal that something is wrong. Margaret is said to have been 24 years older than her husband. If you look at the two daughters mentioned Margaret would have been too old to have been their mother. Nevertheless this 1550 date is all over the internet. The only source is an Email (the couple actually had 11 children, but only four daughters survived as stated on the still surviving monument in their parish church )
Nicholas's father actually died in 1548 and his ipm clearly says " He died 19 Jul 1548. His son and heir was Nicholas Martyn aged 20 on 22 Feb 1549"
The date on the Peerage is twenty years out and when this was used on wiki-tree dates on other family members were entered accordingly. Change one according to the evidence and a whole host of others were now wrong. This date may not have come originally from the Peerage but is certainly perpetuated by it .
Just one example.Obviously,it may not be typical but because the site uses such a variety of sources, there are bound to be others.
Here on wiki-tree, surely we strive for accuracy. Primary sources are key. On wikipedia primary sources are forbidden but the emphasis is more and more,as far as I can see on reputable secondary sources. The Peerage is a tertiary source