And if he forgot save the PDFs or his hard drive gets accidentally hit by a meteor (but the .tax2021 file miraculously survived because it is stored on backup drive)? He's what? Effed? The whole point of software dev (and IT in general) is to avoid disasters by planning for them as part of the software build. That includes backwards compatibility and regression testing. Otherwise. what are we paying $75 for? It sure isn't for the pretty fonts.
