I can be the DP. I got in early on the promo when it dropped and generally followed it through the "evolution" as Amazon probably caught on to what people were buying (i.e. Amazon GCs). When it dropped, I was able to buy $400 of Amazon GCs and $100 Whole Foods for $400.
Then, when word came out that the promo was working a second time for the same account (presumably after Amazon had to perhaps rewrite a few things once they caught on to the "scheme"
), I went in again and was able to get another $300 of third party GCs (SB and Whole Foods again) with the 20% promo applied AGAIN and using the Amazon GCs I bought from the first time
Since I didn't use the full $500 max (I have a hoard of GCs and no matter what the deal was, I didn't need THAT many GCs I thought at the time), and as I was reading some more, others started reporting the promo appeared to be cumulative, I figured I'd give it another try (nothing to lose), I figured I could give my mom some WF GCs since she loves shopping there. I bought the remaining $200 in WF GCs again, but this time, it was hard coded that I couldn't apply my Amazon GCs anymore, BUT the promo applied again. I made a last test purchase just to see if it was capped, and surely, $100 was max, but to churn the first set of Amazon GCs and utilize the 20% twice and on a cumulative basis.