Yang Xi
Although no autograph copies of Yang Xi's famous calligraphy have survived, one well-documented stone rubbing version of the revealed "Huangting jing" (黃庭經, Yellow Court Scripture) has been given special attention. The Song dynasty connoisseur and critic Mi Fu (1051-1107) analyzed four manuscripts of the "Huangting jing", and said the best one was written on a silk scroll with a provenance that he traced back to the early 8th century. Mi disagreed with a former owner Tao Gu (陶穀, 903-970) who said that Wang Xizhi wrote the manuscript, and concluded it was a superb example of calligraphy from the Six Dynasties period. The Ming dynasty calligrapher and painter Dong Qichang (1555-1636) was so impressed by the Mi Fu manuscript that he made a copy, recommend it as the best model for studying "kaishu" script, and included it as the first example in his classic "Xihong tang fatie" (戲鴻堂法帖, Calligraphy Compendium of the Hall of the Playful Goose). Dong's colophon attributed the calligraphy to Yang Xi himself and described it as "the traces of a holy immortal" (Ledderose 1984: 262-263, who calls Dong's attribution to Yang "extremely optimistic").
Quran
In 1972, in a mosque in the city of Sana'a, Yemen, manuscripts were discovered that were later proved to be the most ancient Quranic text known to exist at the time. The Sana'a manuscripts contain palimpsests, a manuscript page from which the text has been washed off to make the parchment reusable again—a practice which was common in ancient times due to scarcity of writing material. However, the faint washed-off underlying text ("scriptio inferior") is still barely visible and believed to be "pre-Uthmanic" Quranic content, while the text written on top ("scriptio superior") is believed to belong to Uthmanic time. Studies using radiocarbon dating indicate that the parchments are dated to the period before 671 CE with a 99 percent probability.
In 2015, fragments of a very early Quran, dating back to 1370 years ago, were discovered in the library of the University of Birmingham, England. According to the tests carried out by Oxford University Radiocarbon Accelerator Unit, "with a probability of more than 95%, the parchment was from between 568 and 645". The manuscript is written in Hijazi script, an early form of written Arabic. This is possibly the earliest extant exemplar of the Quran, but as the tests allow a range of possible dates, it cannot be said with certainty which of the existing versions is the oldest. Saudi scholar Saud al-Sarhan has expressed doubt over the age of the fragments as they contain dots and chapter separators that are believed to have originated later.