Hi,
First of all, which is the year of birth - 1856 or 1868, you have mentioned both.
Secondly, what is the source of this - have you found him on all subsequent censuses and is his year of birth consistant on all?
Thirdly, who are "they" who couldnt find it?
And, have you looked on FreeBMD for the birth?
Sorry for all the questions!