For exmaples 1 and 2:
Whenever you have sabía + que + v2 (secondary verb), there are three options for v2.
One is for the conditional mode, to express that something that was quite probable finally happened: Sabía que podrías.
Another possibility, for the indicative mode: v2 is in pretérito pluscuamperfecto, to show that the action of v2 wich took place in the past is clearly finished: Sabía que habias podido.
And the last one, also for indicative, v2 is equal to 'sabia', both are in pretérito imperfecto. In this case v2 will be all about the present moment, or even about the future: Sabía que podias (ir al cine por ejemplo, ahora, hoy o la semana que viene).
Also, this last case is also aplicable to sabia + que + futuro próximo (ir + a + infinitivo) Sabía que ibas a venir, for exmaple (hoy, o la semana que viene). Notice that the verbo 'ir' is conjugated in pretérito imperfecto too.
If you wanna say the v2 in present, saber will also be conjguated in present. You don't say 'Sabía que tienes un gato', you say 'se que tienes un gato'.
As you might have know, the pretérito imperfecto is used for past actions who had some continuity in the past, so, to say it rough, when you choose 'sabía', it's because you've been knowing (or not knowing) at least for a while. If you know the person for some time, and in all this period you have been ignoring that she or he had a cat, then you've been 'not knowing it' for a while. Same thing that if you knew about a person having a cat, you have been knowing since they told you, until today.
For example 3, they are interchangeable, don't make it complicated.