The FAA 8110-120 does not apply to EASA. Even if there is no extensive series of examples regarding surrendered or abandoned STC, the Agency principle, similar to the TC case, is that in case of surrendered STC, the Agency keeps the responsibility on the TCH holder and will ensure, in the framework of the Continued Airworthiness, the highest level of safety of the products. The EASA role is strictly limited to CAW oversight.
Moreover, EASA is not bound by the FAA Guidelines 8110-120, regarding FOI. EASA is bound by regulation (EC) 1049/2001 on access to documents, which foresees that any member of the public with residence in the EU (but in practice anyone) can request access to documents held by the Agency. The Agency can then decide whether such access might be granted (there are exceptions foreseen in article 4).
Such regulation applies only to already existing documents that the Agency holds (either because EASA is the author or because they have been received by EASA in the framework of its institutional activities).
This regulation does not apply to request for information where the Agency has to compile a new document to put together the aforementioned requested data and/or info.