It is traditionally accepted that adhyatma Ramayana is a part of the brahmanda purana but according to Wikipedia it was written in 14th century.Does that mean it was added later to the brahmanda purana? This website here https://www.wisdomlib.org/hinduism/book/the-brahmanda-purana Doesn't include adhyatma Ramayana in the Translation.Matsya purana Chapter 53 says that brahmanda purana consists of 12,200 verses.If we include adhyatma Ramayana,the number of Verses excede 18000.
Scholars ascribe Adhyatma Ramayana to the period 14th-15th century.
Though depicted as a part of the Brahmanda Purana, respected as a canonical work of the Vaishnavas and begun in the Tantra style of conversation between Siva Mahadeva and Parvati, scholars ascribe it to the period 14th-15th century, A.D. Nothing is known of the author, though the Rama tradition believes it to be Vedavyasa since it is said to be an integral part of the Brahmanda Purana.
A Concise Encyclopedia of Hinduism by Swami Harshananda