If a petition is signed by owners of land, the executive officer shall cause the names of the signers on the petition to be compared with the names of the persons shown as owners of land on the most recent assessment roll being prepared by the county at the time the proponent adopts a resolution of application pursuant to Section 56654 or files a notice of intention to circulate a petition with the executive officer pursuant to subdivision (a) of Section 56700.4 and ascertain, to the extent possible, both of the following: