You can easily access your private posts on Tumblr. You just need to follow the steps which has been explained here.
Access Private Tumblr Posts
Tumblr allows it’s user to create private posts and access them. You can create private post as shown below…
Only the owner of main blog can access or get on those post which has been posted privately. However, If you have created a private post which has been posted on secondary Tumblr blog, those posts can be seen by other admins or members of your secondary blog.