This is extremely late, but I hope helpful nonetheless. I apologize for any typos, as I'm on a phone.

I think it is important to establish that "independent" here may need some defining. Many revolutionary governments' proclamation dates differ from the date their independence was recognized by other states or international organizations. States typically celebrate the day they make they proclaim independence, hence the U.S. celebrates July 4, 1776 and not, say, December 17, 1777 when the French recognized that independence or September 3, 1787 when Britain recognized it.

As I'm sure you know, Indonesia celebrates August 17, 1945, when independence was proclaimed. You hear other dates because the Dutch, in their efforts to reconquer what they deemed their territory, disagreed. Their Western alliance did not recognize Indonesian independence until the Dutch-Indonesian Roundtable Conference (August 23 - November 2, 1949), where terms were negotiated at the end of the war. These agreements were ratified by the two countries and officially sovereignty was transfer on December 27, 1949 (minus Western New Guinea, which the Dutch remained in control of).

So, again, we would need to define independence clearly to really put a date on it. Should we go with the declaration on August 17, 1945? The official transfer of power on December 27? Or the U.S. official recognition of Indonesian independence on December 28, cuz 'Murica?

My personal take is that agreeing with a date in 1949 signifies that the Dutch had some sort of right, ownership, or power over the national unity of Indonesia beyond the use of force. Indonesian unity was decided upon by Indonesians - not the Dutch, the U.N., or anyone else. Thus, i go with the '45 date.

References:

If you can get a hold of them

Merle Ricklefs - A History of Modern Indonesia Since 1300

George Kahin - Nationalism and Revolution in Indonesia

Benedict Anderson - Java in a Time of Revolution