Mehtab Singh Ji,
Bhai Gurdas Ji's works were edited by Bhai Vir Singh (or scholars at later period), also Dasam Granth from 1895. So, it can be that modern scholars edited them so that these works are made according to the (modern) grammar.
I am not sure, but what i am trying to say is: i have read in a book at pairi bindian didn't exist before 1850s. there were only 35 akhars in Gurmukhi, not the extra ones.