You can surely say both.
2-o-o-1 should be more standard, but if, for example, it is room 01 on the 20th floor of a hotel, 20-o-1 would carry that additional information as well.
And of course, there's still the standard "two thousand (and) one".
1 december 2015
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Heb je je antwoorden nog steeds niet gevonden?
Schrijf je vragen op en laat de moedertaalsprekers je helpen!