Hi gotobed,
You can see some comments about “standard sizing” in the industry in post #2 here. While different manufacturers can have different standard sizing or dimensional tolerances for different reasons … and most people would normally return a mattress due to comfort issues … with a 120 day return/refund policy if your mattress is out of spec or even if it’s inside their spec tolerance and you aren’t happy with it for any reason then you can always return it at no cost.
Congratulations on your new mattress 
You certainly made a good quality/value choice and I hope you have the chance to share your comments and feedback when you’ve received it and have had the chance to sleep on it for a bit.
Phoenix