You could have made a note of what the variable names stood for and put it at the top or end of each source file, in a separate file or even on a piece of paper

You could have made a note of what the variable names stood for and put it at the top or end of each source file, in a separate file or even on a piece of paper. There is nothing inherently disadvantagous to using abbreviations as long as you have a key to the abbreviations.