K-2 child's A number?

[TomT]

On the I-485 application to register permanent residence for a derivative beneficiary (a son of the K-1 beneficiary), would one insert the A # of the principal alien (his mother) or leave it blank?

p.s.

Many thanks to the Immigration service for their comprehensive, easy-to-read and easy-to-find instructions.

[Edit to note that I have discovered that, unlike the mother's, a K-2 child's 'A' number will be assigned for the I-797C Notice of Action which indicates receipt of the child's I-485 package. Accordingly, the box for said number should be left blank on Form I-485 because it doesn't exist yet.]

p.s

The confusion lies in a few forms being used for many different immigration situation.