You can go from lo broda to zo'e noi broda in the gadri definition because the definition can choose that this zo'e refers to lo broda. Thus you can go from any lo brodi to zo'e noi brodi as long as you have a zo'e in mind that already refers to exactly what you want. However, in the other direction, it's less true that you can simply replace the strings. Going from zo'e noi broda to lo broda requires the zo'e to refer to lo broda. But not every zo'e refers to lo broda, it takes a special context. If zo'e is tea, then zo'e noi broda won't be lo ckafi. And that's why you cannot take it as a literal replacement.