"Mr Wright laid upon the table the original of the letter of Callinicus Hiermonachos which had, apparently, been written at Alexandria and which had certainly been sent thence to the Guardian office by the ordinary post. Mr Wright proved by comparison of the writing of this letter with other known specimens of the handwriting of Simonides that the letter of Callinicus must have been written by Simonides himself in England and sent hence to someone in Alexandria, who posted it to the Guardian."
"The Guardian, 18 Feb 1863
The basic truth is the impossible knowledge and the historical imperatives that show Simonides and Kallinikos well aware of the manuscript. Including their working at Mount Athos on the same manuscript at exactly the right time in 1841. (Discovered in 1900, Bill Brown amazingly accused this of being a tampered library entry!!) Kallinikos called the 1844 theft perfectly, which nobody else understood (and some even struggle today.)
That combined with the tissues of lies and thefts from Tischendorf and other evidences, like the "coincidence" of the extremely similar Hermas from Simonides before Sinaiticus, (linguistically dubious as an early ms.) demonstrate the Athos creation. And the various palaeographic anomalies and the "phenomenally good condition" and the colouring and stains matching the Kallinikos account and more.
If letters from Kallinikos were edited, or even if they were to some degree Simonides creations, the basic evidence remains Athos, c. 1840. And I actually once had one of the letters in my hand in NYC at the Grolier Club, and may have the pictures still, from years back. When I went back earlier this year, that letter was not in the box. I hope they find it and connect it. There are probably other originals in London or Liverpool. Australia has correspondence from Charles Stewart, who is wrongly accused of being a phantom.
And I get a special smile about Tischendorf anxious about Simonides on his way to St. Catherines in 1859.
Some have written that they had a friendship, even a corroboration, that went south. However, the fact that Simonides was working at the Russian Historical Archives in St. Petersburg in the late 1860s is an evidence that they went back north, or at least had a quid pro quo.