yy

As abbreviations the difference between yy and tt

is that yy is year, in two-digit, numeric format, as in: dd/mm/yy while tt is teetotal.

As an initialism TT is

tuberculin tested (a quality of milk in post-war Britain.

As a noun TT is

time trial.

As abbreviations the difference between rr and yy

is that rr is (aviation|travel|dated) (from the status code used in the gds) reconfirm / reconfirmed while yy is year, in two-digit, numeric format, as in: dd/mm/yy.

As a noun rr

is railroad.

As a proper noun rr

is roraima, a state of brazil.

As abbreviations the difference between yy and yy

is that yy is year, in two-digit, numeric format, as in: dd/mm/yy while yy is year, in two-digit, numeric format, as in: dd/mm/yy.