I posted this in another thread almost a month ago and wanted to resurrect it here since the original thread was in Site Feedback. I was checking over edits and found a couple of rejections on some Wii Item Numbers I submitted recently. Anyway, here's most of the body from the original post...
In addition, for Nintendo products. The item number on the record is supposed to be the item number on the packaging (if it exists, if not then cart/disc number may be used) and not the number on the manual or the cart. Those who put in the cart item number to the main record are allowed, but be aware that it just makes extra work to be done in the future to fix the entry later.
Not trying to make waves but since this was brought up, it might perhaps be a good idea for ALL persons capable of approving/rejecting edits to have a pow-wow of sorts and come to a unified consensus about this because I can recall plenty of times where I've done exactly what you've said and have found my edit to be rejected. I've done edits on previously blank 'Item Number' boxes as well as trying to edit the field where the previous person used the information from the cart instead of the packaging. Once in a while I'll get a rejection kicked backed to me even though I keep seeing what Trip posts so evidently there is a person or persons that isn't on the same page.
Incidentally I've noticed this same behavior in regards to PS4 and Vita Item Numbers. For the longest time I've gone with using the number that appears at the bottom of the spine, much like how we do with PS1, PS2, PS3, and PSP. I know they used to use CUSA numbers but have switched over to a 7-digit number. I've plugged that number into a few entries and sometimes someone will reject it. I know there's other identifying numbers on the packaging and in the case of Vita, the carts themselves have a PCSE number. Anyway, if you're going to have a huddle about the Nintendo Item Numbers then maybe you could also come to an agreement on which PS4/Vita Item Number to use. 
I think it's safe to assume the pow-wow never occurred and there still is no consensus as I got these rejections.
Your edit to Alien Monster Bowling League was rejected.
Tuesday August 1st, 2017 at 6:28 AM
Field: item_number
New Value: RVL-P-SABE
Reason: Information Already on File. Please see the VGCollect Style Guide or visit the Forums to clear up any listing questions.
Your edit to Rayman Raving Rabbids 2 was rejected.
Tuesday August 1st, 2017 at 6:28 AM
Field: item_number
New Value: RVL-P-RY2E
Reason: Information Already on File. Please see the VGCollect Style Guide or visit the Forums to clear up any listing questions.
Along with this one from a couple of days ago...
Your edit to Game Party Champions was rejected.
Friday July 28th, 2017 at 9:46 AM
Field: item_number
New Value: WUP-P-AGPE
Reason: Information Already on File. Please see the VGCollect Style Guide or visit the Forums to clear up any listing questions.
Aside from the dashes, this is how the Item Numbers appear on the packaging.
Also, in each of those rejections I do see where I have approved edits where I added the Disc Item Numbers to the Description field. While I verified with the copies I own physically, sometimes those numbers were already filled in on the current Item Number line and I merely copied/paste once I manually verified it against my copy.
TL;DR Trip has stated on more than one occasion that the Item Number should be the one on the packaging but someone is rejecting edits still. Item Number lines are sometimes already filled in but also sometimes contain incorrect or incomplete info on them. Attempts to fix this are met with rejections.
TL;DR 2: Electric Bugaloo - These rejections also occasionally occur on PS4/Vita Item Numbers because someone sometimes doesn't like the 7-digit numbers on the spine being called the Item Number. PS4/Vita have largely switched to the 7-digit number over the old SLUS/BLUS/CUSA/ULUS Item Number system that PSX/PS2/PS3/PSP employed.
