The term "assignment" is not used in the membership agreement (sorry I answered you hastily off the list using a term from the English language rather than lawyer talk, but it isn't what you are being asked to sign). The "grant of rights" (5.2) states clearly that you "grant to AMICO a non-exclusive, worldwide license" to use the data you provide "solely as part of or in conjunction with the compilation and distribution of the AMICO library". No one else has objected to this clause.

4.2 only refers to 1) that you make annual contributions and 2) that you add no additional condiutions to their use beyond those of the copyright owner if it isn't you. This was part of our agreement last summer to make it possible for end-users to get a license to use the library under consistent terms.