Did the leafless backbulb have its leaves when you bought the plant and how long have you had it . It might just need potting on into some fresh media.
In my experience yellowing of the bottom leaves is the first sign that there is a problem of some sort.
Don't get me wrong the plant is still ok but is not growing to its optimum for some reason . I grow about 2000 seedlings and I import 500 every year so I know how important nutrition is for these
plants
Now if I found a plant in my collection that has lost leaves early like that I would find out what it has caused it .Who ever grew that plant initially did a good job because the first and second bulbs have done well. but if you don't take action now to rectify
the next bulb may smaller, which means that the plant is going backwards.

I bought the plant last may, and re-potted it when I got it, into a small- bark mix (bark and perlite mix). When I bought it, it had one mature growth, with one developing one. The older growth only had 4 leaves total. Over the summer, the new growth grew, and finally the pseudobulb developed in late october. The leafless backbulb shed its leaves in the fall. The new growth hasnt lost any leaves so far, and there is another growth which has been developing since november. All the root growth that I can see from inside the clear pot has occured since I repotted it in early June.

Oh, and I have it in full sun in a south facing window, where it gets quite cool night next to the glass. I have not been feeding it, since from what I have read, watering and fertilizing should be kept to a minimum over the winter.

This is my first cym, your information is very helpful!
Thanks! :)

Are the black spots on the leaves normal for a cym? Mine has the same spots and I've been concerned as this is my first cym. also.

Any thoughts on the last post?

Sorry for taking so long to reply but my Email has been down for a few days.
I get to be so mad when I read books and articles that tell folks to give their cymbidiums a drying out time. those few words have most probably killed more cymbids than all the bugs put together.Many novices take this to mean bone dry and this sets the plant back, as it has yours. the fact is CYMBIDIUM HYBRIDS SHOULD NEVER BE COMPLETELY DRY . That is why so many growers around the world grow their plants standing in a saucer of water
In the winter months I warm the water to about 16 degrees C using an aquarium heater. I the summer months I don't allow the water temperature to exceed 23 degree so I cool the water using frozen bottles of water . So I think if you just give that plant some water and don't let it dry out it will do well for you.

Chris , if you are talking about the black marks on the base of the leaves - that is quite normal for a cymbid.

I'll second one comment Des made - that plant looks too dry to me. I personally try to keep my cymbidiums at 6.5 to 6.8 pH. Thats the pH of the water that I keep in the saucer under my cymbidiums. If pH gets to 6 roots start to die. Health of the plant deteriorates at about 7.2. I look at my cymbidiums everyday all 2000 or so of them and pull off dead leaves. Dont worry if one plant is loosing one leaf but worry a lot and find our why one plant is loosing a lot of leaves. Gypsum, dolomite lime, and crushed oyster shell keeps my pots at the proper pH. I use a tablespoon of each for each gallon pot. I do monitor pH. Have discussed why this works with a chemist friend of mine.
Close pH control may not be so critical with a lot of orchids but it is with cymbidiums and any other orchid you keep moist all the time (my 2 cents worth).

Oh cool, I'm glad to hear it's normal. I've been worried that I have a problem...thanks