Fidelity Research FR7F history/changes

Recently fell in love with a front end I was supposed to be trying to sell for a friend that included this cartridge. Wonderful bass,dynamics, delineation of instruments with nice harmonics,... I bought the front end & recently bought a back up cartridge as well. What prompts the question is the minor cosmetic differences (believe they both are 6 digit serial numbers) - the 1st one (the magic 1) has a vertical stripe in front and seems to have a slightly different body size (the stylus guard of the 2nd cartridge does not quite fit; and the marked playback differences-the 2nd cart does not have the "technicolor" presentation of the 1st. It is OK but not what I was hoping for(It was supposed to have low hours and I saw nothing under the scope to contradict that). If there are experts or resources out there to fill me in, please do since when the time comes to retip, I assume that the magic might go away & I may need to hunt down another one & will need to figure out what criteria to look for to make sure I do not buy another that has less magic. Best wishes, LS