Adjusting Amazon pre-orders may alter your delivery time

I ordered a record on Amazon via Prime four days ago. The shipping time was showing "Arriving March 19-March 25". While I was browsing on Amazon yesterday, I noticed that the item I ordered was no longer available on Amazon to purchase through Prime and I decided to check my shipping time on my order and make sure I was still receiving it. The order was still showing a shipping time of "Arriving March 19-March 25". My birthday is coming up and I had been given an Amazon gift card, which I had just loaded to my account. When I looked at my pending order I noticed there was an option to apply my gift card to the total and since my debit card hadn't been charged yet, I decided to apply my gift card balance to the order. As soon as I hit the "apply" button to the order, my shipping time immediately changed to "Arriving April 3 - May 3".

I called Amazon and they had no way of changing my ship time back and were very poor at explaining what happened. On the first call the woman I spoke to just tried to tell me that the shipping time changed on the item, which I thought was miraculous, since it happened the instant I added the gift card payment. On the second phone call, the woman I spoke to said that someone "bought the record" in the instant I added my gift card payment, which changed my shipping time, which didn't make sense, since the item wasn't available for Prime shipping before I added my gift card.

After my first phone call with Amazon I found multiple threads on Reddit where people had pre-ordered items on Amazon and when they updated the payment on their yet-to-ship orders, they lost the shipping timeline they had previously seen on their order. Someone on one of the Reddit threads said that an Amazon rep he spoke to said that changing your order that has yet to ship treats it as the newest order for that item, so you get bumped to the last availability that was in Amazon's system for that order. That seems ridiculous, but makes sense. I wish someone on Amazon's end of things would have admitted that and explained it to me when I called them. After talking to the second Amazon rep, she said they definitely do have my item, but that the item is in a UK warehouse, so the shipping will take longer. I should still be getting the record, but I thought I would share this info, so others can avoid the same mistake I made. It seems pretty ridiculous that me paying earlier than necessary with my gift card essentially moved my delivery time back a month.