I've understood it that Ludwig went from white to clear in '68-'69ish, then to granitone in '71ish, then back to clear in '76, then 6-ply in late '76ish-'77. I have a BDP kit I'm working on that's bass drum is 1970 and rack toms are 1976 and all are 3 ply with clear interiors.
Yes at least on the first part. I have another kit with keystone badges, clear interiors, and stamped November 1969. I have a 1968 orphan floor tom with white interior. My 1976 Ludwigs don't have date stamps, but they do have clear interiors.