"Having a diagnosis of PDA is helpful for a number of reasons.

It helps people with PDA (and their families) to understand why they experience certain difficulties and what they can do about them.
It allows people to access services, support and appropriate advice about management strategies.
It avoids other incorrect diagnoses (eg attachment anxiety disorder, ODD, emotional and behavioural problems or having a wilful and naughty child).
It warns local authorities that this diagnosis can sometimes result a high exclusion rate unless sufficient support is provided.
One parent described to us how "it was a huge consolation to find a set of characteristics and criteria that seemed to have been made for my child here was a tailor-made paper on my child."

Having a diagnosis would not allow more people access to services.  Because there is a lack of services.