North Borneo Block Of 4 Stamp Imper And Printed On Gum Side?

Hi,nice to see you all again,I have not been logging here for such a long time and miss you all.

I found two block of four british north borneo stamps.The two block of four stamps are 1889 rose-pink 4c and also 1918 brown-black 1c stamps.The block of four 1889 4c stamps were imperforated holes(horizontal and vertically)without cancelled to order(CTO)Normally has cancelled to order on any british north borneo block of four stamps and were printed on very thin paper.Beside that,the other 1918 block of four 1c stamps printed on gum side(there are no gum on behind)I have never seen any british north borneo stamps printed on gum side before.

Are this block of four stamps considered as error or variety stamps?Rare or common block of four stamps imperforated holes and printed on gum side since this are not listed in stanley gibbons,scott and other stamps catalogue.this two block of stamps were not been certified by any stamps expert or specialist yet,So I need help from a stamp expert or specialist to help me to identify them,help is always apprieiciated,thanks in advanced.