We begin with the classic late 50s lineup. Silent-Supers in colours, along with the Sterling and Skyriter in grey and green.
One change is made to the lineup of manual portables: updating the Skyriter to give it white keys and a slightly modified logo.
Now the Galaxie is introduced with the white front panel.
One year later, 1959 models are still being sold (likely just old stock).
Sold alongside the new Galaxie, of course.
By 1962 the Galaxie has superseded the Silent-Super entirely, and a modified Sterling (probably introduced in 1961) is sold. The Skyriter is updated once more (now made in England as well).
Galaxie remains unchanged, the Skyriter is replaced by the Corsair, and the Sterling gets a facelift. Also, the introduction of the Coronet electric.
One year later there are no changes, but the old Electric is still being sold.
Galaxie II is introduced, with the jeweled bearing and Change-A-Type.
Same Galaxie II unchanged for the next year.
Super Sterling now replaces the Sterling in a Galaxie-style body. Corsair has red function keys.
The Galaxie Deluxe with tabulator bar and half/rapid spacing is introduced, possibly in 1967.
No apparent change for 1969.
This is by no means comprehensive, or for that matter totally accurate, but it's what I could gather with advertisements! I hope that it will be helpful for dating your 1970s SCM machines. It also shows that SCM sold older typewriters longer than I'd previously known.