Here is a concise, Jain-dharmic overview:

• What they are: In Jain tradition, the 14 Purvas (Purvas) are said to be the earliest Jain scriptures, composed in the very ancient period. They were memorized and handed down orally for generations before being written down in later centuries, according to many Digambara accounts.
• Why they’re “lost”: Traditional sources say the Purvas became unavailable or were intentionally concealed/blotted out over time, especially around events like the Bhadrabahu era and the southward migration. Because of this, there is no single, universally accepted surviving text that is called “the 14 Purvas” today.
• What they covered: The Purvas are said to have encompassed a wide range of subjects—ethics (moral conduct), cosmology, metaphysics, logic, grammar, and spiritual practices. They laid the groundwork for later Jain philosophy and conduct.
• Digambar vs. Śvetāmbara stance: There is a difference in emphasis and tradition between Digambaras and Śvetāmbaras regarding the Purvas. Digambaras traditionally stress their ancient origin and loss, while Śvetāmbaras often rely on later canonical compilations. The exact enumeration and contents can vary between traditions.
• Current status: Because the original Purvas are not extant as a complete, agreed-upon corpus, modern Jain scholars and practitioners teach using the later canonical texts that reflect, reinterpret, or summarize the themes of the Purvas.

If you’d like, I can share more on how specific topics from the Purvas are treated in current Jain ethics and philosophy, or point you to a traditional enumeration as cited by a particular Jain tradition.