I may be posting this in the wrong forum, not sure where I belong on this but either way... How does a coin get assigned a reference number? Say for instance a cud, I posted one a little while back and used a site @SensibleSal66 shared and I found my exact cud error on the site but it doesn't have a reference number but all the other examples do.
I'm not familiar with "reference numbers". My best guess is that term would be used by someone who is creating a personal list. Someone else creating their list could use different reference numbers. Just a guess.
@Mark68 this is actually the one I have. It's a 74. as you can see there's no reference number below it.
The reference number at the top is the attribution number for the coin. The cross reference numbers are ether obsolete numbers used in the past or numbers used by someone else.
Many that do make up their own cross reference # is for personal commercial reasons ( such as labeling and selling) as well as the reflection of their knowledge. IMO, if you have such a coin ~GREAT! if not, they might sell you one. but be aware if it is not universally known, you likely could not reclaim the value if selling in the future. IMO of course. Jim
In general, reference numbers are assigned by experts in particular series, errors, etc. Anyone could use their own, but likely noone else would use them unless they were an authority on the type. Also, I find most reference numbers trivial for my type of collecting aside from KM#'s, but if you decide to specialize in certain series/types, then you may well need to know reference number for that specialty.
We are all looking towards the member that has also seen and documented the same coin. It is not a quick process.