I found an interesting article telling about this scroll:
The papyrus roll containing the first part of De Pietate was among those covered by the eruption of Vesuvius that buried Herculaneum, with its Villa of the Papyri, in A.D. 79. These carbonized scrolls were so distorted and damaged that the original excavators mistook them for lumps of charcoal. In 1787 the roll containing De Pietate was opened.
1997.12.19, Philodemus, On Piety Part 1. – Bryn Mawr Classical Review
Enter now the malign gods of chance, muddle, and scholarship. When the first part of De Pietate was cut open, the two halves were for some reason given different catalog numbers and transcribed separately, with an interval of nearly two decades separating the transcriptions. One half, designated P.Herc. 1077, was drawn on two separate occasions between 1787 and 1809; shortly afterwards, the Rev. John Hayter absconded with several fragments of papyrus and the complete set of apographs, which are now in the Bodleian. The Bourbon government of Naples had another set of drawings made from the surviving fragments, but not before the edges of the outer half had been somehow severely damaged. Not until 1825 did the Italian technicians move on to P.Herc. 1098, the other half of the original roll, now believed to be a separate document.
