Yes, there was an "internal reflection improvement". It involves a rubbery matte substance called "PALPAS". I believe it also was supposed to dampen sound, which it does to some extent. Nice idea, but PALPAS deteriorates over time, developing vein-like cracks that criss-cross its surface. My 503CX is about 15 years old, and the PALPAS has started to go. The immediate cure is a bit of flat-black model paint on the cracks. The long-term cure is replacement, which requires a major body disassembly. I'm going with flat-black paint until the body needs a CLA.
Other than that, my CX is wonderful. I bought it as part of a kit. I don't use the metering system. Otherwise I would have bought a 501CM. I do find the viewfinder image cutoff a bit annoying.