For the first two seasons (at least) the Stephens' had that candleabra on the piece of furniture in the entryway by the front door.

Then, right in the middle of it all, there is one episode where there is a mirror instead (not the big one they had later). It was in "Speak the Truth," fifty episodes into the show. Then in the very next episode and for at least the rest of season two, they went back to the candleabra.

I guess they just used it for the "mirror, mirror" routine in the opening scene where Endora appears as Sam's reflection. It couldn't have just been that it was aired out of sequence since there were twenty-four more episodes filmed after that one in season two.

Does anyone know when they switched to the big mirror for good? I remember it being used in several storylines in later seasons.

I only have seasons 1 & 2 so far so I can't check it out.

You only see it for the first two seasons. Then they use the mirror and the "Girl With Broom" painting in that spot, usually with a plant on the table.