(b) Such endorsement shall stipulate that the plat does not conflict with the county official map, where one exists, or, in cases where plats do front on or have access to or are otherwise related to roads or drainage systems shown on the county official map, that such plat has been approved in the manner specified by subdivision two of section two hundred thirty-nine-f of the general municipal law. 2. Notification of filing. It shall be the duty of the county clerk or register to notify the planning board in writing within three days of the filing or recording of any plat approved by such planning board, identifying such plat by its title, date of filing or recording, and official file number. 3. Effect of filing. After such plat is approved and filed, the streets, highways and parks shown on such plat shall be and become a part of the official map or plan of the town. 4. Cession or dedication of streets, highways or parks. (a) All streets, highways or parks shown on a filed or recorded plat are offered for dedication to the public unless the owner of the affected land, or the owner's agent, makes a notation on the plat to the contrary prior to final plat approval. Any street, highway or park shown on a filed or recorded plat shall be deemed to be private until such time as it has been formally accepted by a resolution of the local legislative body, or until it has been condemned by the town for use as a public street, highway or park.

(b) In the event that such approved plat is not filed or recorded prior to the expiration date of the plat approval as provided in section two hundred seventy-six of this article, then such offer of dedication shall be deemed to be invalid, void and of no effect on and after such expiration date.