AFAIK, your 1 to 5 are indeed from the UK. They aren't listed in the ordinary Gibbons Commonwealth catalogue, but it's possible they might be in a specialised catalogue. However, cut squares aren't generally popular in most Commonwealth countries. The preference is for the entire original item.
No.6 is indeed from British India: it's part of a ¼ Anna postcard. They were printed in the (probably) billions. Not listed in Gibbons, but it could be from any one of #1 to #6 in Higgins & Gage. The complete mint cards are all minimal value, so this cut square is of no monetary value at all, I'm afraid.
This is what one version of the complete card looked like:

(Used in conjunction with a Jammu & Kashmir ¼ Anna brown)