I have literature here being some years old and there are some differences between black to platinum. Grado at least some years ago did state that the cartridges are selected. So all Greens were said to be selected from the Blacks - only 10% of the Blacks make it to the Green selection, i think - and the Greens are selected to the Blues and so on.
This is what my literature says:
I had to fill in the dashes, because the software running this side seems to eat blanks. And it doesn´t even get the dashes right, it looks good as i write it, but in preview its messy - have fun finding the collum.
The rest of the specs appears to be the same. At least there is no special note on the styluses - but Grado at least did mention that the better models do have a better cantilever also having fewer moving mass, i think the moving mass of a Silver is like 10% reduced in comparison to a Red.
The problem now with the specs is that some sellers do confuse them. For example there was one seller claiming all Grados from Black-Gold having channel separation of 35DB - while another seller did claim Grados from Black-Gold having 25DB channel separation only. This stuck in my head as i bought a Gold for having a rather high channel separation, which is 35DB.
In addition to that some aspects of a cartridge are related to the cartridge body. A Black surely will perform better having a Silver stylus for example, but things like channel separation and i think frequency range also are related to how precise the coils in the cartridge-body are positioned.
This should mean that a Black having a Silver stylus will track better as the Silver stylus is said to have fewer moving mass and a better cantilever, but channel separation and frequency range still should correspond to a Black.
This also should explain why they select the Blues from the Greens for example, as they check for frequency range - and the cartridge having FR of 10-55k has its coils more precise positioned than the cartridge having FR 10-50k only.
Therefore the bodys from Black-Platinum shouldn´t be alike.