Some companies don't but there nothing stopping you from pursuing it yourself.
Sharing from experiences of dealing with debt
The greatness of a man is not in how much wealth he acquires, but in his integrity and his ability to affect those around him positively.
Bob Marley. http://kallis3.blogs.iva.co.uk
You cannot make them -- though ( for one in particular I know of) it might well come back and bite them later on, unless there has been some form of rather unorthidox agreement with creditors behind the scenes.
If you do want this investigated and paid in you could do it yourself for at least the crediotrs you remember. I would not advocate using a claims company yourself as you could find yourself liable for the fees.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014