I used to do migrations between library systems, and often they'd export from the old system as CSV. One rule I gave them was "never open this file in excel", because they'd always try to be helpful by tidying something and I'd end up with scientific notation ISBNs, dates that were in one form if they could be coerced into US-style infix, otherwise left in the original form, barcodes losing zeros, etc. etc.

The same problem happens with UK phone numbers, where the leading 0 gets chopped off Solvable if there's a space between the dialling code and the number, but when individuals enter their number, they don't always do this

Don't ISBNs also contain an X sometimes?

The old ISBN10 standard could get X (meaning 10) as the last character (the last number is a check digit), but ISBN13 (which prefixes 978 or 979 to ) is all numbers. The check digit is calculated differently. One obvious advantage is that the ISBN13 is barcode compatible.

I would guess that most modern actors in the book business has been primarily using ISBN13 for at least the last decade.

Thanks! The last time I read about ISBNs was probably more than a decade ago.

X can be a check digit. From memory the check digit is calculated using a modulo 11 calculation.