Gyani ji,
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/history-of-sikhism/451-punj-granthi.html

I had a look at Guru Granth Sahib ji (1353) onwards for the Salok Sahiskriti Mahla 1. Also there is Mahla 5. Just to be clear does this mean that these saloks are creation of First and Fifth Guru?
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=451

At least the bani you mentioned here, sounds like gurumukhi only, 1354 onwards, there seems to be more sanskrit words (I dont know, but looks like!)

Regards.