cc, for example, has a new gloss as "complimentary copy," now that carbon copies are a distant memory.
Jackie asks : When and how did the word gloss come to be used in this sense, please?
OED says : "a similar explanation of a word in a glossary or dictionary. Also, (more widely) a comment, an explanation, an interpretation, a paraphrase. A collection of such words, a glossary, an interlinear translation or series of annotations. A disingenuous explanation, comment on or explain a word, read a different sense into" and it goes on and on.
That any help?
I have, and sometimes use, a typewriter which is handy when power fails! Not too long ago had to visit three stationery stores before finding one that still *stocks carbon paper!