You're going to see two
types of numbers in coin descriptions.
1) One or more reference book numbers to the
type of the coin (think of this as
car model, not a specific
car) (e.g. "
Vlasto 123")
2) Sometimes also a sales
history of the specific coin, giving an
auction name and item number
How many reference numbers are given depend on the
type of the coin. If there is a single authoritative reference book (eg.
Roman Imperial Coins =
RIC) that covers this
type of coin, then maybe there'll only be one reference number. If there are multiple reference books (by different authors) that cover this
type of coin, then you may see more than one reference quoted.
In your example, there are three reference books cited that include this
type:
Vlasto, HNI and
SNG ANS. Each reference book is going to have it's own
type numbering scheme, so if you
had the references available and were to look up "
Vlasto # 123", and "
SNG ANS # 1234" you'd see them both describe the same
type as the coin being referred to.
It should be obvious if a coin description is referring to a prior sale (giving the name of an
auction house), or a reference book (giving the name of the reference). If in doubt
FORVM's
NumisWiki can
help, as it should have entries for all the
standard references. In this case if you look up "
Vlasto" you'll see that its actually an author's name, but also used as shorthand to refer to a famous reference that he wrote.
https://www.forumancientcoins.com/numiswiki/view.asp?key=Vlasto