If you are using the I2C version of the library, then you would be using that with a backpack connected to the I2C pins A4 and A5. And you would be extremely lucky if that worked at all since there are a number of different I2C backpacks which use different wiring and port addresses. Or did you already realise that?
Your second version specifies all of the important parameters instead of taking a wager that your present backpack actually does match the library default.
You are however advised to forget those older libraries, and use bperrybap, Bill's HD44780 library which can be automatically installed using the library manager in the IDE and has a test program which will figure out all the settings for you.