Question: In what year was the cathedral, that Arnao de Vergara produced several windows for, registered as a World Heritage Site?

Context paragraphs:
Białowieża Forest: Białowieża Forest (Belarusian: Белавежская пушча, "Biełaviežskaja Pušča" ; Polish: "Puszcza Białowieska"   ] ; Russian: Беловежская пуща, "Belovezhskaya Pushcha" ) is one of the last and largest remaining parts of the immense primeval forest that once stretched across the European Plain.  The forest is home to 800 European bison, Europe's heaviest land animal.  UNESCO’s Man and the Biosphere Programme (MAB) designated the Polish Biosphere Reserve "Białowieża " in 1976 and the Belarusian Biosphere Reserve "Belovezhskaya Puschcha " in 1993.  In 2015, the Belarusian Biosphere Reserve occupied the area of 216,200 ha , subdivided into transition, buffer and core zones.  The forest has been designated a UNESCO World Heritage Site and an EU Natura 2000 Special Area of Conservation.  The World Heritage Committee by its decision of June 2014 approved the extension of the UNESCO World Heritage site “Belovezhskaya Pushcha/Białowieża Forest, Belarus, Poland”, which became “Białowieża Forest, Belarus, Poland”.  It straddles the border between Poland (Podlaskie Voivodeship) and Belarus (Brest and Grodno "voblast "s), and is 70 km north of Brest, Belarus and 62 km southeast of Białystok, Poland.  The Białowieża Forest World Heritage site covers a total area of 141,885 ha .

Saint Sophia's Cathedral, Kiev: Saint Sophia Cathedral in Kiev is an outstanding architectural monument of Kievan Rus'.  The cathedral is one of the city's best known landmarks and the first heritage site in Ukraine to be inscribed on the World Heritage List along with the "Kiev Cave Monastery" complex.  Aside from its main building, the cathedral includes an ensemble of supporting structures such as a bell tower and the House of Metropolitan.  In 2011 the historic site was reassigned from the jurisdiction of the Ministry of Regional Development of Ukraine to the Ministry of Culture of Ukraine.  One of the reasons for the move was the fact that both Saint Sophia Cathedra and Kiev Pechersk Lavra are recognized by the UNESCO World Heritage Program as one complex, while in Ukraine the two were governed by different government entities.

Arnao de Vergara: Arnao de Vergara was a 16th-century Spanish master glassmaker.  Between 1525 and 1536 he produced several windows for Seville Cathedral, many of which survive, before later moving to Granada.

Seville Cathedral: The Cathedral of Saint Mary of the See (Spanish: "Catedral de Santa María de la Sede" ), better known as Seville Cathedral, is a Roman Catholic cathedral in Seville (Andalusia, Spain).  It was registered in 1987 by UNESCO as a World Heritage Site, along with the Alcázar palace complex and the General Archive of the Indies.  "See" refers to the episcopal see, i.e., the bishop's ecclesiastical jurisdiction.

Cornwall and West Devon Mining Landscape: The Cornwall and West Devon Mining Landscape is a World Heritage Site which includes select mining landscapes in Cornwall and West Devon in the south west of England.  The site was added to the World Heritage List during the 30th Session of the UNESCO World Heritage Committee in Vilnius, July 2006.  Following plans in 2011 to restart mining at South Crofty, and to build a supermarket at Hayle Harbour, the World Heritage Committee drafted a decision in 2014 to put the site on the List of World Heritage in Danger, but this was rejected at the 38th Committee Session at Doha, Qatar (July 2014), in favour of a follow-up Reactive Monitoring Mission.

Nicolás de Vergara el Mozo: Nicolás de Vergara el Mozo (1540–1606) was a Spanish sculptor, architect, ironworker and glazier, most notable for his work on religious buildings, including Toledo Cathedral.  He was the nephew of the master glaziers Arnao de Vergara and Arnao de Flandes and grandson of Arnao de Flandes the Elder.

Waldschlösschen Bridge: The Waldschlösschen Bridge (German: Waldschlößchenbrücke or Waldschlösschenbrücke ) is a road bridge across the Elbe river in Dresden.  The bridge was intended to remedy inner-city traffic congestion.  Its construction was highly controversial, as the Dresden Elbe Valley had been declared a UNESCO World Heritage Site and UNESCO expressed strong concerns against the bridge, noting its intent to withdraw the World Heritage title if the bridge were built.  As a result of this project, the Dresden Elbe Valley was listed in 2006 as an "Endangered World Heritage Site" (one of two in Europe, the Medieval Monuments in Kosovo being the other one), and in 2009 became only the second World Heritage Site to be de-listed.

Arnao de Flandes: Arnao de Flandes (literally "Arnao of Flanders") or Arnao de Flandes the Elder was a master glassmaker born in Flanders at an unknown date in the second half of the 15th century.  He is believed to have moved to Spain between 1480 and 1490 and set up a workshop in Burgos, producing work for Avila Cathedral (1497), Palencia Cathedral (1503) and Burgos Cathedral (1511–1515).

Rapa Nui National Park: Rapa Nui National Park is a national park and UNESCO-inscribed World Heritage Site located on Easter Island, Chile.  Rapa Nui is the Polynesian name of Easter Island; its Spanish name is Isla de Pascua.  The island is located in the southeastern Pacific Ocean, at the southeastern extremity of the Polynesian Triangle.  The island was taken over by Chile in 1888.  Its fame and World Heritage status arise from the 887 extant stone statues known by the name "moai", whose creation is attributed to the early Rapa Nui people who inhabited the island around 300 AD.  Much of the island has been declared as Rapa Nui National Park which, on 22 March 1996, UNESCO designated a World Heritage Site under cultural criteria (i), (iii), & (v).  The park is under the administrative control of the Corporación Nacional Forestal (CONAF), which provides legal protection to the total area of the island.  As Easter Island has insufficient resources for conserving its natural heritage, the Government of Chile and the National Council of Monuments have provided financial support for the conservation efforts.

Bahrain Pearling Trail: The Bahrain Pearling Trail or Bahrain Pearling Pathway is a serial cultural heritage site inscribed on the UNESCO World Heritage List in 2012.  It consists of 3 oyster beds in the Bahrain northern waters, a segment of the coast and the seafront Bu Mahir fortress in the southern tip of Muharraq, and 17 buildings in Muharraq historical town connected by a 3.5 km visitor pathway.  The Site was inscribed as a UNESCO World Heritage Site on June 30, 2012 and is Bahrain's second World Heritage Site after the Bahrain Fort.

Supporting paragraphs: Arnao de Vergara Seville Cathedral
Answer: 1987