Why cant I find these deaths on Scotlands People?

[Forfarian]

This is very confusing now. His death certificate states he's Colin Dow Murchison, widower of Margaret Arthur. His Parents are Donald Murchison & Flora MacLeod. Yet all their census returns, their children's names etc are Dow. I wonder why he dropped the Murchison and one of the children had it as his middle name at her marriage? 

Could he have been illegitimate? That might account for switching surnames.

Is his mother named on his death certificate as Flora Murchison MS MacLeod, or just as Flora MacLeod?

Or is there an error in whatever transcription of the census you are using? Have you checked the original census documents?

[wivenhoe]

"His death certificate states he's Colin Dow Murchison"

Who is the informant?

[phenolphthalein]

I have noticed that death certificates are often transcriptions of the time. 
The responce of the bereaved to whoever asks the question may depemd on how it is asked.
The transcriber of handwritten notes for the formal certificate may misread their own or another's handwriting.

I have seen a marriage at Port Macquarie recorded as Port Mercury due to accent of the informant.
I have seen a son as informant give his own parents' names rather than those of his deceased father.
I have seen Thomas misindexed as James.

Another thing to consider is did the person gain a step-father at some stage of their life -- might explain them being known by 2 names.  or did they adopt the Dow surname for inheritance reasons or to distinguish them from others of the same name in their locality,
Another thing could be two lines of handwritten information transcribed as one -- eg if the next death had the previiously unknown surname or two different columns of information were combined into one. maybe the 2nd forename was incorrectly transcribed into the surname box or a location etc

Random ideas
pH