While I generally agree with the timeline, based on my own observations about the texts on the body, I believe the metal grip 970x was contemporary with the plastic grip 971x, which must have been its cheaper counterpart (also partially sliding sleeve on the 970x vs fixed for the 971x), see my post here:
Just like the older 9505 + 9515.
Another thing to consider is the cone. Longer and tapered at the tip for the early checkered version and most examples of the grooved version. However some late circular grooved grip versions ( those that also have the color coded stripes at the back) have a simpler, shorter conical tip. The third version of the 970x with the stamped metal grip, with longitudinal grooves inspired by the plastic 971x, only comes with the short conical tip.
@drifand , can you post a photo of them with the cones unscrewed and clutch visible?