I have a hard time with either option, because I can’t see a case where you would have an initial review date without also having a last review date. I can see the opposite scenario, which would mean you haven’t done a review yet, but both scenarios have a previous a previous review date if you have a planned review date.
What would make sense is “IRD LRD [PRD],” where the brackets indicate what is optional. If the initial review date is needed, it should always be needed. Otherwise, just call it the previous review date, which would automatically be the initial review date if you’ve only had one review.
The way it is currently written, I would not know in either interpretation when to execute which side of the OR. When should I display the initial review date instead of the previous review date? The only scenario that makes sense to me is the one mentioned above, but, as I said, there’s no reason to mention the initial review date in that scenario.
All that said, I did initially read the first interpretation. I see the comma as being used to separate parameters. Just like in, say, a list of names: “John, Marsha, Amy Jo, James.” Fortunately, I wouldn’t have had a clue how to implement that, and would still have to ask for clarification.