With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: The historical calving grounds were unknown but might have been along southern Chinese coasts from Zhejiang and Fujian Province to Guangdong, especially south of Hailing Island and to near Hong Kong. Possibilities include Daya Bay, Wailou Harbour on Leizhou Peninsula, and possibly as far south as Hainan Province and Guangxi, particularly around Hainan Island. These areas are at the southwestern end of the known range. The full extent of the whales' historical range cannot be determined with certainty, but it is known that they at least reached the southern edge of the Gulf of Tonkin. In addition, the existence of historical calving ground on Taiwan and Penghu Islands (with some fossil records and captures), and any presence in other areas outside of the known ranges off Babuyan Islands in Philippines and coastal Vietnamese waters beyond the Gulf of Tonkin are unknown. There is only one confirmed record of accidentally killing of the species in Vietnam, at Ngoc Vung Island off Ha Long Bay in 1994 and the skeleton is on exhibition at the Quang Ninh Provincial Historical Museum. Gray whales are known to occur in Taiwan Strait even in recent years.
text_B: Does this passage suggest that fossils or other remains of this species of whale have been found in the Gulf of Tonkin, which allows scientists to conclude that whales once regularly swam in those waters?
YES.