Copyright © 2005 xxxxx Limited. All Rights Reserved.

S.17(1) to (5) of the Copyright Ordinance states that the duration of copyright of literary, dramatic, musical and artistic works is the life of the author plus 50 years, or 50 years from the end of the year in which the work was first created or made available to the public if the identity of the author is not known or if the copyright belongs to a business entity (ie. a company).
The "2005" in your example is there to indicate the year in which the work was first created or made available to the public. Therefore the copyright of that particular piece of work will expire 50 years later - ie. in the year 2055 in this case.
This "year" is a constant and is not to be changed every year.