JJonahJ

The issue isn't whether or not you've had another Amex card recently, either opened or closed. The concerning factor is whether or not you've closed the exact same card recently (Personal Gold is NOT the same as Personal Plat), and now want to reapply for it again, in which case you'd want to be at least 60 days beyond the exact same prior card's closure, or for more safety 90 days - 180 days.

Since you have not had a Personal Plat card for at least 2 years, you should be good on this front, which brings us to the next potential issue. Ever since July 2015, Amex added notes to the footnotes/T&C, stating only one welcome bonus per card, and it's at their discretion on whether they will give it to you again or not. However, since that time almost everyone has been able to re-open a second time (churned) and still got the full welcome bonus after meeting the minimum spending requirement (MSR). There have been some growing frequencies of reported datapoints where someone was advised by Amex that they would not get the bonus again, and in some of those cases (particularly in 2015-2017) the cardholder still did get the welcome bonus anyways.

You should also be aware that the Personal Platinum card no longer has the quirky benefit of claiming a $200 annual travel credit over 2 years (eg, once for 2018 and once for 2019), within a cardholder's membership year. Now Amex has revised the policy and beginning Jan 1, 2019 it will be only ONE $200 travel per cardholder membership year. So if that was a factor in your choice to open the Personal Platinum, then the lowest you can bring the $699/yr AF down to is $499/yr.