I know Google Translate is completely unreliable, but I hope it at least got the basics of what your comment says. Yes, you can tell the era based on not only the position of his whiskers, but there are a lot of other general features... Earliest 1979 episodes, up to maybe 82 or so, have a very stylized and cartoony unique feel. Doraemon's voice is also totally unique and bubbly. Starting around 1983 and up to probably 86 or so, they sort of tried to stabilize his look [though it wasn't finalized]. His whiskers moved up and around the edge of his face, and his mouth started gaining a triangular feel to it. His voice was still scratchy but was starting to become more less cartoony and bubbly. From then onwards, They moved the whiskers right back to the white part of his face, and his mouth had become more or less fully triangular. He lost his cartooniness and seemed to have been rounded down to appear more childlike. They did that with his voice too, making it more monotonous and slow-paced, but also high pitched, and he lost the scratchiness that classic Oyama had. That only became flanderized as the series kept going, until they discontinued it in 2005.