Different product barcodes in different marketplaces

I am an amazon seller that has mainly sold in the US and Canada. Upon creating a UK listing last year of my main product, I generated the product barcode and found that it was different from the US and Canadian ones, displaying a different ASIN and different barcode.

Now, a year later, I am actually ready to send inventory to the UK, and upon generating a barcode for the same item, im finding that the new UK barcode is the same as my US and Canada one. I am a bit concerned about this. Why would the barcode and ASIN change over the course of the year? would it change again arbitrarily? I do not want to be in a position where my inventory arrives and they say that the barcodes on every unit are wrong.

Anyone experienced this? Thanks in advance!