You should be able to do this--we do something similar, but generically for foreign annuities (as opposed to CN-specific ones):
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Set up the <CN Annuity Due> task to have a RespondBy date that uses the later of 12 months from issue date OR 12 months from triggering task RespondBy date.
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Set up the triggering for it to have two alternative triggers:
a) When a CN application gets an issue date (or the issue date changes, if you want to be more conservative) OR
b) When a <CN Annuity Due> task completes while the status field in the matter does not include "Expired." If you want, you can tweak this to be "when a <CN Annuity Due> task completes with a "Completed" or "Missed" state--that way you can close the task out with "Abandoned" if you are letting it go and it won't generate the next deadline. <CN Annuity Due> would be whatever you decide to call this task (you're actually recursively triggering it based on itself). NOTE: You may get an extra <CN Annuity Due> task at the end of the patent term that dockets before expiration but for date after it is expired. There's probably a way to deal with this, but I haven't devoted brain power to figuring it out at this time.
I also recommend setting up a <CN Annuity Due - Grace Period> task that triggers whenever the <CN Annuity Due> task completes with a "Missed" status. It would be set to have a RespondBy of 18 months from the TriggeringTask Reference Date. If you set up the <CN Annuity Due> task to auto-close with "Missed," then AppColl should, if you miss an annuity payment, auto-docket both the next annuity deadline AND the final deadline for the current annuity deadline.
Disclaimer: While I think that the above will work as desired, you should, if you attempt the above, test it thoroughly to make sure that it behaves as expected. I make no warranties about whether the above information is correct and assume no responsibility for any damages or liabilities that you may incur if you act on the above information/advice.