re-send order details is different from orig email

I updated the text on the initial completed order “thank you” email and update this text:
‘Your order has been received and is now being processed. Your order details are shown below for your reference:’

with some instructions for our product and that works fine when the initial “Thank you for your order” is sent.

If I go to an order and resend the “customer invoice” email in case a customer lost that original email and needs the instructions again, I don’t get the exact same email.
Instead of the “thank you” text is shows “Order XXX details” in the blue header and the text that is usually at the top before the details table “Your order has been received and is now being processed. Your order details are shown below for your reference” is missing?

Its sends the order details but its not the exact same message as the 1st original thank you receipt.

I don’t see a order details email in the list under settings>email but if I look in the email template folder I do see a email-order-details.php which I thought I could edit but didn’t seem to work?

If I resend the “customer invoice” email, how can add some text to the top of that message when it re-sends the order details? Make sense 🙂