Bhagat ji

A comparative study can be done. The differences, yes, reflect the changes in historical facts and conditions, as well as the cultural realities of northern India in the times of either Guru.

However, just last week in reading portions of Dasam Granth I saw many places where the thinking of the Nanaks, in particular Guru Nanak, were reflected and echoed. The voice of Nanak X is his own, as is the poetic phrasing, and there are language differences. Again, there are sections of Dasam Granth that are unique to that scripture. But look again at Jap Sahib and other parts of the Guru's Bani -- and then realize that the imagery, the truths so evoked, many other things are consistent with Adi Granth, but given in a creative and new way.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/sikh-sikhi-sikhism/41-teachings-guru-nanak-dev-ji-guru.html
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=41

This is a discussion that would be very interesting.