What is the number (UFID?) on each music cd?

[Larry Alkoff]

On every music cd is a is a text string printed on the jewel case and 
usually also on the cd itself.

For example, I have two cds by the group Steppenwolf marked:
Steppenwolf    Born to be Wild        MCAD-31020    and
Steppenwolf    The Second        MCAD-31021

Both cds were produced by MCA Records which I believe explains the MCAD 
part.
Both cds were in a series which I believe is related to the consecutive 
numbers.

My questions:

1.  Are these text strings the UFID field in the id3v2 specification?
2.  Can Amarok access the field for reading or writing?
3.  Do you know the purpose of these strings?

I am in the process of purchasing and ripping cds to mp3.
When I shop for new cds I carry a list of my currently owned cds
and that number will help me to avoid duplicates.

Thanks for any information.
Larry