No they were just examples.
Do'n i ddim - you'd use this whenever you'd say "I wasn't" in English.
The second meaning (gwybod etc) is lengthy to explain so please bear with me:
Wnes i - i didn't = a completed event. It happened, it's done. Wnes i ddim gwylio'r ffilm - i didn't watch the film (one off event)
Do'n i ddim - i wasn't = an ongoing event or lasts over time.
Do'n I ddim yn gwylio'r ffilm (pan aeth y sinema o dan dŵr)- i wasn't watching the film (when the cinema flooded)
So in Welsh knowing something wasn't a one off "do'n I ddim yn gwybod sut i stopio siarad amdano" - i didn't know how to stop talking about it.
There are a few words like this:
And more that I can't think of...Sorry!
Clear as mud?