Gigantic Annual #2

Colour Comics' Gigantic Annual #2 was published in 1959 and features a cover illustrated by Hart Amos:

As we know, Gigantic Annuals were comprised of coverless returns from newsagencies, and my copy contains the following issues:

Mighty The 100 Page Comic! #9, c.January 1959 

The Hundred Comic Monthly #28, c.January 1959 

Century The 100 Page Comic Monthly #34, c.March 1959 

James' copy also contains issues from the first quarter of 1959. 

I'm interested in collating the contents of other copies of this and other issues of Gigantic Annual and Mammoth Annual in the interests of ascertaining whether they were published mid-year or at the end of the year. The early Mammoth Annual covers were Christmas-themed, and some issues do have advertiser's date codes on the covers, all of which help in dating some issues in this series. 

I'm also curious if there are editions with variances in the advertisements on the rear cover and inner covers as per my copies of Gigantic Annual #5. My copy has a Stamps of Approval (Seven Seas Stamps) ad on the inner front cover; 

A Weirdo's ad on the inner rear cover;

and a Tommy Steele Guitar Club ad on the rear cover:

Gigantic Annual ran for 16 issues until 1975, and this issue is the only one in the series not to include Annual in the title.

Update 5/1.2020: Mark Muller's copy contains Century The 100 Page Comic Monthly #34 c.March 1959; The Hundred Comic Monthly #28 c.January 1959; and Five-Score Comic Monthly #10 c.February 1959.