Stamping multiple metals

Hello Orchid, I have a few questions about stamping pieces that
employ multiple metals. First, if I have rolled 18g bimetal down to
24g, is it still 1/20 18k, or have I changed the composition by
rolling it out? Second, if my piece is primarily silver with 18k and
22k elements, can I mark all the elements in a row on the silver or
do I need to stamp the bezel 18k, the silver sterling and the gold
element 22k? Or, can I take a a tag of sorts (made of fine silver –
just to make things more confusing) that has all the stamps in a row
next to my signature stamp and solder it to the main body of the
piece? Thank you for your input! Karin