1. 1897 or, more probably, 1898. Note that BPG has used mourning paper (black edges). This may put the letter near his father's death (March 24, 1897), but it may simply be leftover paper that Grenfell had at hand.
2. Also known as the Nubayrah Stele. See also here.
3. U. Bouriant (1885), "La stèle 5576 du Musée du Boulaq et l'inscription de Rosette," Recueil de travaux VI: 1-20.
4. "E" in "Epiphanes" overwrites "P" (possibly from "Ptolemy").
8. B.P. Grenfell (1899), "Strack's 'Dynasty of the Ptolemies'," CR 13.1: 54-56.
9. P.P. = Petrie Papyri. It looks like he wrote 'II' and then canceled this and inserted "the" before P.P. and a question mark in front of his cancellation. Smyly is not mentioned in the review just mentioned, which came out in Feb. 1899, so the letter probably dates to 1898.
10. “slate” = “criticize severely" (J.G. Keenan).
11. The excursus appears in P.Oxy. II, pp. 238-241.
12. To "have someone on toast" is to have control or power over them.
16. This corresponds to l. 25 of the edition.