I broadly agree with my professional colleagues though one view is that there is no time limit - for BOTH - to issue credit-notes u/s 34 (1) as well as for declaring them in returns. As per this view, time-limit prescribed u/s 34 (2) is applicable if issuer wants to adjust his tax-liability (i.e. against such credit-notes issued and declared). Anyway, there is no material change on account of such different views (& I am not sure if portal allows such disclosure beyond time-limit prescribed u/s 34 (2))
However, in my view, issuance of credit-note u/s 34 is OPTIONAL and not compulsory. So, once time-limit prescribed u/s 34 (2) is passed, it is better NOT to issue credit-note u/s 34 at all but issue financial / commercial / accounting credit-note for 'BASIC AMOUNT' towards reduction of / discount in 'taxable value' BUT NO GST on such 'basic amount' should be considered while issuing such credit-notes.
This is with the understanding that underlying supply is indeed made and credit-note is only for reduction of value for any reason (i.e. not for cancellation of supply per se). And if so, recipient need not have to reverse proportionate ITC against such financial / commercial / accounting credit-note and there will not be any loss of GST (which was paid at time of supply i.e. against tax-invoice) to the supplier as well.
These are ex facie views of mine and the same should not be construed as professional advice / suggestion.