Point of taxation

As per POT rules, if invoice is issued within 30 days, POT is invoice date/ payment date which ever is earlier. If invoice not issued within 30 days of completion of service, POT is date of completion of service/ payment date which ever is earlier. (a) What is the POT in the above situation if payment is not received. Can we take Invoice date as POT? (b) What is the POT in the above situation if invoice is issued beyond 30 day limit and payment is not received. Can we take date of completion of service as POT? 

Yes date of completion of service would be date of boking liabity in absence of payment and invoice date bieng beyong 30 days.