Comprehensive WCAG conformance leads to accessibility for all irrespective of the technology used-any statement to prove this legally?

Dear all,

By way of a quick introduction, I am Amar Jain, a corporate lawyer and a 
Certified Professional in Web Accessibility based out of India.

We have a case going on for inaccessibility of our tax submission 
portal. The vendor is Infosys, and the problem is that only those issues 
that we are highlighting are getting resolved and comprehensive audit is 
not being done due to commercial reasons.

Further, there seems to be hard coding for NVDA, as the portal is 
reasonably functional with NVDA and not with Jaws. The lack of audit is 
also leaving behind persons with other disabilities.

The argument of the vendor is that it is because of the architecture of 
the portal which is why NVDA will be the only screen reader which should 
be used for maximum functionality. Second argument is more legal in 
nature, which is to say that current Indian standards only restrict 
testing with NVDA which we can work around.

We need to prove to the Court that a comprehensive WCAG conformance is 
technology independent and irrespective of the technology that people 
use, a comprehensive conformance will ensure widest accessibility 
possible.

Is there any document which backs-up this statement and is there any 
precedent where comprehensive audit has been asked by way of a court 
order?

In nutshell, I need to convince the court that a comprehensive audit is 
the only way to go, and a comprehensive conformance to WCAG will not 
produce different results with different technologies in terms of 
accessibility.

Your valuable inputs will be greatly appreciated before September 22.

Regards,

Amar Jain