Hi, Jill.
Thank you for your questions. :)
Setting different pathways is a little tricky. We don't fully support this at this moment in time for certifications, however, there may be a way you could achieve this using programs and audiences (depending on the version your site is on).
You could set up separate programs for A, B, C and D and assign dynamic audiences to each one where the rules are based on program completion on a fixed date or before/within/after a period of time.
For example, let's say the criteria for program B was for program A to have been completed and that assignment should take place one year after completion of program A. You could set an audience rule (assigned to program B) that audience membership is granted (and therefore the user is assigned to program B) if program A was completed "before previous 365 days". This would display the ruleset as User's program completion date is more than 365 day(s) ago "Program fullname 101". Anyone who completed program A more than one year ago would then be assigned to program B. You could then apply the same process to program C and D.
The only concern I would have is what happens after the completion of program D. Does the program end or do they start all over again at program A after program D? Do users need to be displayed as being certified or simply complete? Knowing the answers to these questions might determine whether using programs and audiences is a plausible solution or not.
Having the ability to specify multiple recertification paths has come up before and there was some discussion about this in the community some time ago now. It's not been something that has come up very often over the years but certainly growing in popularity.
It would be fantastic if you could share a little more about your scenario, the problems you foresee at the moment and what the end result might look like for you. We can take this information back to our Product team for consideration when building out any requirements for this in the future should it be considered.
Thanks.
Tom