Serial number/серийный номер

Did you verify the serial number on the Bottom Case matches the serial number reported by the Logic Board?

Also, try to manually type in the serial number since sometimes I find certain sites may not always like having information copied & pasted since sometimes it may bring in a hidden formatting character making sure you are reading the serial number correctly. Try pasting the serial number into Text Edit....highlight it and change the font to "Menlo" which can make it easier to distinguish between similar characters & numbers so you can manually enter the numbers onto the Apple site.

Even if the serial number was never registered, I think it should still populate the model information and possibly the manufacturing date since Apple would have a record of all the serial numbers it used.

Copy & paste the system serial number since some characters can be difficult to tell apart, for example:

1 & l (the number one and the lower case L), 2 & Z, 5 & S, 6 & G, 8 & B, 0 and O (zero & the letter "Oh"), etc.