Basically there’s 3 types of testing: unit testing (testing that individual components do what they are supposed to do); integral testing (testing that components are working together as they are supposed to do); and, operational testing (testing that the app is operating as it’s supposed to).
If the initial design was lacking then unit and integral testing are “impossible”. That only leaves operational testing. If a bug is discovered not only do you have to fix the bug, retrograde testing also needs to be done (to make sure you didn’t break something else) as well as including the test for the bug in all future testing.
Does Lectora get more that operational testing? (My guess is “no”.)