It has to do with how Magento allocates Sales Order numbers. It's entirely normal to have one out of sequence like that, be previous to the ...
I've gone back through the order number records and found that Magento seems ... if months later they successfully place an order, they get the 'old' increment is. ... I'm trying to decide if Magento should be used as my platform for e-commerce ...
Customer's order number (previous-current), Rank of customer's previous order concatenated with the rank of this order, separated by a - character. Calculated ...
You can see this effect sometimes in the order numbers as they come in on a busy store - occassionally a really old order id comes through in the day's orders ...
The three old sites were using the same Magento numeric series.
previous order; Customer is trying again for a new order (with or
Easily Set a Custom Order Number in Magento With My Free
The above answer is too old and there is drawback of this answer that it
Remember to check the box before “Use Order Status As Default”.
But more importantly, support for PHP 5.6 has already expired. PHP is