Question: What year was the Sunda clouded leopard classified as a separate species than its mainland relative, the clouded leopard?

Context paragraphs:
Clouded leopard: The clouded leopard ("Neofelis nebulosa") is a wild cat occurring from the Himalayan foothills through mainland Southeast Asia into China.  Since 2008, it is listed as Vulnerable on the IUCN Red List.  Its total population is suspected to be fewer than 10,000 mature individuals, with a decreasing population trend, and no single population numbering more than 1,000 adults.  The clouded leopard is the state animal of the Indian state of Meghalaya.

Kamlang Wildlife Sanctuary: The Kamlang Wildlife Sanctuary, established in 1989, is rich in flora and fauna.  It is situated in the Lohit District of the northeastern Indian state of Arunachal Pradesh.  The park is named after the Kamlang River which flows through it.  The Mishmi, Digaru, and Mizo tribal people who reside around the periphery of the sanctuary claim their descent from the King Rukmo of the epic Mahabharata.  They believe in a myth of an invisible god known as "Suto Phenkhenynon jamalu".  An important body of water in the sanctuary is the Glow Lake.  Located in tropical and sub-tropical climatic zones, the sanctuary is the habitat of the four big cat species of India: tiger, leopard, clouded leopard and snow leopard.

Sichuan Giant Panda Sanctuaries: The Sichuan Giant Panda Sanctuaries () located in southwest Sichuan province of China, is the home to more than 30% of the world's highly endangered giant pandas and is among the most important sites for the captive breeding of these pandas.  It covers 9245 km with seven nature reserves and nine scenic parks in the Qionglai and Jiajin Mountains.  Along with the giant panda, the sanctuary is a refuge to other endangered species such as the red panda, the snow leopard, and the clouded leopard.  Outside of the tropical rainforests, it is among the botanically richest sites of the world, and is home to between 5,000 and 6,000 species of flora.  It has been noted that the region is similar to the paleo-tropic forests of the Tertiary Era.

Neofelis diardi diardi: Neofelis diardi diardi is a subspecies of the Sunda clouded leopard ("Neofelis diardi") native to the Batu and Sumatran islands of Indonesia.  It is different to "Neofelis diardi borneensis", which is native to the island of Borneo.

Big cat: The informal term "big cat" is typically used to refer to any of the four largest (living) members of the entire "Panthera" genus.  Among the five total species within the "Panthera" genus, these four are the only cats that are able to roar.  In descending order of their maximum potential size, these four species are: tigers, lions, jaguars, and leopards, with the tiger ("Panthera tigris") being the largest.  A more liberal and expansive definition is sometimes used which may include the snow leopard, puma, clouded leopard, Sunda clouded leopard and/or cheetah, although these added species do not roar.

Formosan clouded leopard: The Formosan clouded leopard ("Neofelis nebulosa brachyura") is a clouded leopard subspecies that is endemic to the island of Taiwan.  A camera trapping study carried out in the largest remaining lowland primary forest in southern Taiwan during 2000 to 2004 did not reveal the presence of a clouded leopard.

Sunda clouded leopard: The Sunda clouded leopard ("Neofelis diardi"), also known as the Sundaland clouded leopard, is a medium-sized wild cat found in two Indonesian islands of Borneo and Sumatra.  In 2006, it was classified as a separate species, distinct from its continental relative "Neofelis nebulosa".

Mehao Wildlife Sanctuary: Mehao Wildlife Sanctuary is a 282 km2 wildlife sanctuary in the Lower Dibang Valley district of Arunachal Pradesh, a state in Northeast India.  The sanctuary was declared in 1980, and is home to many species of wild animals including the Bengal tiger, hoolock gibbon, leopard and clouded leopard.

Neofelis: Neofelis is a genus comprising two extant felid species from Southeast Asia: the clouded leopard ("Neofelis nebulosa") of mainland Asia, and the Sunda clouded leopard ("Neofelis diardi") of Sumatra and Borneo.

Neofelis diardi borneensis: Neofelis diardi borneensis is a subspecies of the Sunda clouded leopard ("Neofelis diardi") native to the island of Borneo.  It is different from "Neofelis diardi diardi" in the shape and frequency of spots, as well as in craniomandibular and dental characters.

Supporting paragraphs: Neofelis Sunda clouded leopard
Answer: 2006