My short answer is "No, I have no idea"
My long answer:
For the past ten years, I have been using the same ballpark working assumptions when used car shopping:
1yr/10,000 miles 81%
2 yr/20,000 miles 69%
3yr/30,000 miles 58%
These % are based off current MSRP of new equivalent models. I have been using them for ten years and they have served me well when negotiating. I'm not even sure where I got them from originally. Combination of running some numbers and research on lease residual values.
They are a benchmark in my mind for negotiation. Typically, Porsche dealers will give a million reasons on why "Porsches are different...yadda, yadda, yadda" but inevitably, I always get the car I want at a price that fits in my framework..OK sometimes it takes two days...
Usually I see dealer "ask" prices 5-10% higher than this but I can get them down with a bit of effort. Even after they tell me I'm "nuts" and "not a chance"
So in my opinion the "matrix" will continue to be the best first guess, at this point. I don't think there is enough solid information to say anything else.
There are a number of factors that offset the percents like bid/ask, CPO, condition, short term fluctuations... but I think the average is still a good place to start. If you are selling a car, it is going to be lower than these numbers, IMO. ( I think many guys who trade in a car don't even know what they got because they are buying a new car and fail to account for what they could get a for a discount off MSRP) e.g. I ordered my 718 GTS for more than 10% discount from MSRP without a trade-in.
Interestingly, if I look prices of 2015/16 Cayman GTS they seem to fit the pattern.
Black Book Weekly Values Lite
I have no reason to believe that the 718 will be any different, regardless of internet chatter about the four cylinder, etc.
Not sure where you got your numbers but they look a little high to me. Maybe you are using original MSRP. I prefer to use "current" because i think it is a better benchmark for "value" but they still shouldn't differ by that much of the the short time frame.
Warning: This is all my own personal voodoo but it has consistently worked for me. Yes there are some outliers like the Spyder and GT4 but many times these are temporary aberrations. I wouldn't expect anything like that for an S or GTS model given the availability.
I don't even know why people think the GTS holds value( as a %) better than the S. Not in my experience. Dealers may try to ask for more but I not convinced they get it out the door.
Finally I do have a tendency to buy my cars in December thinking I can get a better deal. My point being that the residuals probably have a good deal of variation in then due to a multitude of factors.
In the end, the lease residuals will impact decisions and thus help determine supply demand.
Is 67% really the residual for a three year/10,000 mile lease?