Giza and Dahshur may both be incorrect; Meidum may be the true nexus of Petrie’s confusion.
”With Cheops we are faced with no real discrepancy: the Turin Papyrus gives 23 years whereas the records reach up to the 12th (An example of a 17th count was argued by Petrie; however, it is probable that he was confused on this matter)20. In this case one may argue for a biennial system. After all, this is a new reign and the practices of Snefru need not have been followed. It is unfortunate that Cairo Fragment No. 2 of the Annals does not preserve any dates and that none of the nine listed cases present a “year after the Xth occurrence” or any connection with cattle.
20 A History of Egypt10, Lauer is adverse to this reference: in: BIFAO 73, 1973, 134, n. 1; cf. Stadelmann, in: MDAIK 43, 1986, 239. I suspect that Petrie confused his data and mixed the evidence from Snefru at Meidum (where there are cases of zp 17: nos. 13-15 in our list under that king) with that of Cheops at Giza”
From the ”Addendum: Meidum Dates”:
”The following are the graffiti listed by Posener-Kriéger that should be added to our analysis. Those without dates are ignored. All relate to Snefru.
(5) Year of the 17 occurrence: Graffiti A 12-21 with A 23-26 to be added possibly A 22 is to be set in the same group.”
Source: “Dated Texts of the Old Kingdom”, Anthony Spalinger, Studien zur Altägyptischen Kultur © 1994, Pages 285, 318 and 319.
Note to the serious student: The whole of the article contains scholarly merit. In particular, the Addendum contains cogent discourse ”concerning the intricate question of regnal year dating in the Old Kingdom”, amplifying a transitional intercalation from the ‘cattle count’, while recognizing the import of the maturing organizational bureaucracy.
“Quis custodiet ipsos custodes?“ - Decimus Junius Juvenalis
“Numero, Pondere et Mensura“