I have multiple Wilson ProStaff Tour 90 racquets (non-nCoded) and have just recently noticed that the paintjob on one of them is differnet from the other two (I bought them all separately). The throats of the two similar racquets have a large Wilson signature in silver on one side while the differing racquet has the words Double-Braid. The paintjob finish on the two similar racquets is dull compared to the differing one, which is rather glossy. Also, the two similar racquets have three letters on the buttcup of GFU and GGZ, while the differeing racquet is GFX? What does this mean? If it just different production time periods? Do the racquets differ in composition (It seems the two similar racquets feels somewhat hollow compared to the differing racquet; any advice on fixing?)? Answers would be greatly appreciated. Thanks.