If you are happy with what they shipped to you, that's great. But it isn't a proper 1973 seat. It is a 1970-1972 seat. I know because I bought that seat from YamahaXS650.com for my 1971.
1973 is a one-year only seat. There are several differences between it and the earlier seats. The most important is how it meets the gas tank. If you are using a 1973 tank, then you need a 1973 seat for it to look right.