It's definitely true that they do not have access to the original OS/2 source - this has been confirmed by people from Arca Noae in various interviews/presentations I've seen. I've never heard a definitive explanation for why, but two reasons are usually speculated:

1) Due to the amount of third party code in OS/2 (most notably, the DOS and Win 3.x layer) that IBM is unable to license out the code, or unwilling to go to the trouble to figure out the legal implications.

2) IBM has lost some or all of the source code.

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TheCondor 4 hours ago | parent | next [-]

You couldn't convince me that IBM lost it..

The licensing would be my guess, Microsoft owned some of the code, there may have been other third party code in there too.

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projektfu 2 hours ago | parent | prev [-]

Did eComStation also lack access to the source? Weird.

	▲	ch_123 2 hours ago \| parent [-]
		As far as I know, yes. There were no changes made to eCS which required source - everything was implemented as drivers, or layers on top of the base OS.