Question: When was the self-described "neoceltic pagan folk" band based in the Netherlands formed?

Context articles: Ymyrgar
Spiral Dance (band)
Geology of the Netherlands
Kūlgrinda (band)
Faun (band)
Moonsorrow
Cesair
Sine Missione
Žalvarinis
Omnia (band)

Ymyrgar is a pagan folk Metal band from Tunisia founded in 2012, as the first folk metal band in Africa.
 Their name is inspired by the primordial giant Ymir who is the ancestor of all Jötnar according to the poetic and prose Edda.
Spiral Dance is an Adelaide-based Pagan folk rock band whose musical focus is on the concepts of magic, myth and legend.
The geology of the Netherlands describes the geological sequence of the Netherlands.
 Large parts of the Netherlands today are below sea level and have in the past been covered by the sea or flooded at regular intervals.
 The modern Netherlands formed as a result of the interplay of the four main rivers (Rhine, Meuse, Schelde and IJssel) and the influence of the North Sea.
 The Netherlands is mostly composed of deltaic, coastal and eolian derived sediments during the Pleistocene glacial and interglacial periods.
Kūlgrinda is a neofolk/pagan folk band from Vilnius, Lithuania, established in 1990 by Inja and Jonas Trinkūnas.
 The band owes its name to "kūlgrinda" – a secret Samogitian underwater causeway.
Faun is a German band formed in 1998 who play pagan folk, darkwave and medieval music.
 The originality of their music style is that they fall back to "old" instruments, and the singing is always the center of attention.
 The vocals are performed in a variety of languages, including German, Latin, Greek, and Scandinavian languages.
 Their instruments include Celtic harp, Swedish nyckelharpa, hurdy-gurdy, bagpipes, cittern, flutes and many others.
 In june 2017, the band played in the Czech Republic for the first time at the MeetFactory venue.
Moonsorrow is a Finnish pagan metal band formed in Helsinki in 1995.
 Musically, the band incorporates elements of black metal and folk metal in their sound.
 The band call their sound "epic heathen metal" and try to distance themselves from the term "Viking metal".
 They have distanced themselves from other folk metal bands, emphasising that their music is pagan and spiritual and is challenging for its listeners, rather than happy or danceable.
 The band members have varying levels of pagan belief but they draw on pagan spirituality for lyrics and inspiration.
Cesair is a Dutch band formed in 2008 who make pagan folk, world fusion and world music.
 They are the main representatives of the pagan folk music scene in the Netherlands, alongside pagan folk band Omnia.
 The band refer to their genre as “Epic Folk & Mythic Music”.
 They perform on a variety of modern and traditional instruments, including accordion, hurdy-gurdy, hammered dulcimer, Irish bouzouki, violin, cello, bodhrán and many others.
 Their songs are performed in a variety of languages ranging from Arabic, medieval Celtic languages, English, Latin, Greek, to Middle Dutch, Old Norse and more.
Sine Missione (Latin: "Without mercy" ) is the first album by Dutch Pagan folk band Omnia, recorded in 1999 and released in 2000.
 It was supposed to be an archeologically and historically promotional CD and not to be used for the popular market.
 It contains constructions of Roman and Gallo-Roman music.
 At this point Omnia was a theatre group (combat and ritual performances) of 8 to 14 people.
Žalvarinis (English: made from brass) is a folk rock band from Vilnius, Lithuania.
 They were formed in 2001 as a collaboration between the pagan metal group Ugnėlakis and the pagan folk group Kūlgrinda.
 This was reflected in the title of their debut album in 2002, "Ugnėlakis su Kūlgrinda".
Omnia is a self-described "neoceltic pagan folk" band based in the Netherlands and whose members over the years have had Irish, Dutch, Cornish, Belgian and Persian backgrounds.
 Their music takes on the form of various cultural routes, from places around the world such as Ireland, England, Cornwall and Persia.