1968 Transitional Dime

There were multiple varieties of collars used for 10 cent coins.
There is a "scallop" one with wide smooth top and bottoms of the grooves.
There is a "cogwheel" with sharp V-shaped tops and bottoms (like on the photo 3 posts above)
There is a "flat top" with wide flat tops and very shallow grooves (like notches)
There is a "flat bottom" with wide tops and bottoms (but still is slightly V-shaped).
I have seen both "scallop" and "flat bottom" on 1966 cents.
I have all 4 types in 1968 PL sets (which are all Ottawa). Sorry, I cannot make any good photo through the pliofilm.
I have 1969 and 1970 10 cents with "cogwheel" and "flat top".
Some coins have rounded edges with grooves shorter than the coin thickness, others have rectangular edges with grooves coming into the rim ("flat tops" in particular).

That makes me to believe that the entire Flat vs V-shaped criteria for differentiating Ottawa and Philadelphia coins was made by mistake.
Probably the theory originators had a specific sample from Phili mint with coins of one type only.
Another observation is that flat-bottom coins are much harder to find, while with the about same mintage there should be an equal amount of each kind.
And the original article about those coins was telling that USA dimes collars were used. But those are different in shape, size, and number of grooves.
I have not seen any 10 cent coin with dime-style grooves.

In my sample of 1969 10 cents, most have flat-bottom grooves. I guess there was a new batch of collars made closer to the end of 1968.

A comparison sound test (Ping test) would confirm if it is in fact 80%
silver. I trust them since they graded it, but hearing it would be
so satisfying... This is the first time I hear such a transitional
error for 1968, and I'll ping each one I end up finding.
How much is it? I'd like to have one if possible...
Luc