Good questions Stefano. You already show that you have a good general idea of the meanings. Let's see examples of the usage of these transitional phrases. Notwithstanding that you already show a general idea about the meaning and use, I will proceed to show you something about these words. I could quote something from a book, but barring that, I can rely entirely upon my own familiarity with the terms to communicate how they can be employed in our writing. Notwithstanding, that there are more qualified people who can answer this question, I will give it a try. Barring that however, certainly somebody may quotes something from some text or other which will answer you. Notwithstanding that there are websites also that can explain the use of these words, I will show something. I could cite something from a website myself, but barring that, we can struggle along with these few examples. In fact, there could be a financial disaster or a calamity in the weather that will prohibit me from answering, but barring that Stefano, I can offer some assistance to you.

Really good question.