Neither the rating nor the barcode thing is definitive, in other words you are correct
sometimes but not all of the time. There are instances where the same barcode is used in different countries. As far as I can tell, the usage of barcode seems to be relating to the publisher, and a publisher may not opt for a new barcode in another country if it doesn't have to. So try to remember to never expect that the barcode is going to be different because sometimes it isn't.
For rating, again it depends. Sometimes a publisher may decide to release the UK version to EU, or not make a separate version for EU and UK and then the EU version is the same and has the BBFC rating. There are also times where a publisher does it the opposite way, where the version sold in UK is the "EU" version and thus has the ELPSA rating on it and no BBFC rating. The instances beyond that is when a publisher or distributor uses BBFC rating labels on EU/ELSPA rated titles.
In any case, as for rejects it depends on the particular instance. If you submit and edit and it gets rejected post into the Listing Error thread:
https://vgcollect.com/forum/index.php/topic,10555.0.htmlPut the item link in the post, and what you tried to change (and to what) and then we can review it and say why it happened. Sometimes it happens by mistake, or sometimes because we need to research it for later and reject it so it doesn't stay in the queue. Other times it is because previous info on the entry prohibits changing the data you tried to put.