hi, i'll go to it. i have some philatelic books by gibbs, grainger and mackay. written for adults but doesn't exclude children.
looking over the pages of singapore i do notice different perfs which i understand.
i do have some used or i would say well-worn stamps that i got out of a circuit book for 20c avg. no corners missing. i enjoy looking at the postmarks that show part of the word singapore. it tells me the stamp did it's postal duty.
i am quite aware of cto's. several books mention it. i knew these stamps were "suspect" as a young adult. if collectors like 'em, i won't "rain on their parade".
closing, i have us plate blocks of stamps i've enjoyed looking at. my fav's- kansas statehood and traffic safety from the mid-60's. if i go back into topical/thematic collecting i will collect only the one's i enjoy looking. it might be willy-nilly but i don't want to make it too restrictive.
i appreciate you sharing.
ps. i might register at stampboards site.