The constellations you see at night are constantly changing through the Year because the Earth is orbiting the Sun. you probably are never going to see both the constellations Scorpius and Orion at the same time in the same sky unless Scorpius is setting and Orion is rising,, and i think December is the wrong time of year for that to be possible..
The "galactic plane" isn't Labled on the sky. if you saw what i call the winter Milky Way, the Orion Arm, congrtulations, because tyou mist have had clear skies with low artificial light pollution and no Moon. There's only one place I am familiar in Arbuckle buntains in Oklahoma On the turn outs of I-35 that i know I MIGHT be able to see the orion Arn of the Milky Way galaxy. Earth and the Sun are IN the orion Arm. Seing the Sagittarius Arm of the Milky way Galxy, The Sunner milky Way and the two dust lanes that mirge into one dutalane I am pretty familiar with But that is in june July and August and Scorpius and Antares are my "guide stars to finding the summer Milky Way..
You must have had low artificial light pollution and great seeing. THAT is why there were more stars.and different stars The Big and Little dipper asterisms are in different places in the sky in summer and winter too. In the northern hemisphere.You are also older than you used to be and are becoming more familiar with the stars at night. By "More clusters' i assume you mean the Pleiades and the Hyades, both in the constellation Taurus, which is a winter constellation, and that you might be using binoculars, are you may have very good vision. with no cataracts.
The stars ARE different in winter and summer. They've ALWAYS been there, but you may never have "SEEN' them before. It IS pretty awe inspiring when that happens to you ,especially the first time, no matter how old you are..
Edit: Sagittarius is a SUMMER constellation in the U.K.. It is NOT a winter constellation..