You went from an A (or "A.5"?) to a C? Granted, I'm a guy, so it's hard for me to imagine, but that sounds like the smaller size must have been horribly uncomfortable. I'm really curious if somebody can describe what that's like. I'm imagining stuffing my feet into shoes that are 2 sizes two small every day or something. Is it like, you've conditioned yourself to it over the years and don't even notice the discomfort until you find something that fits correctly?
A cupsize without a bandsize is literally meaningless if you are trying to imagine what the breasts look like. It is a misconception that a D is always bigger than a C is always bigger than a B, etc. A 32D is the same amount of breast as a 34C, which is the same amount of breast that a 36B is, but on different frames. Surprisingly few people know this - both men and women. Lots of women say things like "My breasts can't possibly be Ds! I fit into these A-cups!" but that's because they don't actually understand how bra sizing works.
Bras sizing works by (roughly) describing the ratio between the ribcage and the bust measurements. In a perfect world where all manufacturers sized the same, cup sizing would be something like an A cup is a 1" difference, B: 2", C: 3", etc. The band size represents the ribcage measurement (Usually not literally, though, due to stretchy fabrics and manufacturer sizing. I've found that the band size is, on average, two to four inches bigger than ribcage measurements IRL.)
In addition to the above, which you could probably figure out on your own, the same cup size on a different band size accommodates a different volume of breast tissue.
So if someone says they are a 32C and someone else says they are a 36C, the second girl will have "bigger" breasts. Think of it this way: while the difference between their ribcage and bust on both of them is 3", the second girl's ribcage is wider so the total circumference of her bust is 4" bigger than the 32C girl, which "allows" for more breast tissue.
You can easily see this by actually looking at different bras. The cup (and real breast tissue) always starts near the armpit and ends near the center, regardless of what size it is - if there is more ribcage than there will be more cup (and therefore more breast).
You can actually adjust for different ribcages when you want to compare breast size. You drop a size from the band and go up a size in cup (or vice versa), and those breasts will be roughly the same volume. A 34A and a 32B is roughly the same amount of breast tissue, just one is on a smaller frame.
It is very common for women to have too large a band and too small a cup. For most women they don't notice because their breasts are being fully and comfortably covered, but since their band is way too loose they are not getting any support. As they go through the down-band-up-cup process, their band can get a lot smaller and subsequently the cup gets a lot bigger. They were originally using a bra cup size that could accommodate the same volume (via having a larger band) but for the wrong body type. When they finally get a bra that is built for their body type, not only are they finally being supported by a properly fitting band, but the molded cup actually mimics their own breasts. That's why a lot of girls say they look AND feel so much better.