The assumption that all would be forgiven after confession, especially deathbed confessions, is not true, because it is an incomplete process of redemption.

Confession is simply an admission of guilt to the breaking of spiritual law in sin; a first step in taking responsibility for the harm (caused by sin to self and victims).  

It is the beginning of healing and freeing the soul (from the chains of sins in the unholy) which begins with the truth in confessing the wrongs.   

By limiting the redemption to first steps, it often makes it impossible to receive the salvation, because the process of redemption is incomplete.  

One does not fully clean oneself up and repair the damages to the spirit in one's character and it fails to make amends to victims of the sins of harm; therefore, there is no redemption.  

Half measures are like half truths, except in this case, confession does not even reach the halfway mark in the redemption process.

For example, if you are an alcoholic, you must first confess and admit that you are, before the process of healing can begin; however, it is just step one of a twelve step process.  

You cannot get totally clean from only step one.

You have to get to the root causes and root out the problems, just as you have to root out sin and self-causes or temptations of the sin.

Therefore, the first steps towards forgiveness in redemption is not forgiveness itself.  

Confessions, especially deathbed confessions, should not be presented as if it is.