Sorry to reply from the office with the login sand15.
Mistake ot not mistake ?
I would even say mistakes.
You wrote "I simply looked at the graph the OP wanted to fit and "eyeballed" a few obvious points through which the graph passed."
As a rule it's already a very bad idea, specially when you already have numerical values at hand (the one the OP used).
Next, it's not your job, nor mine, not the job of anyone else to replace, as you did, data by one's own data. If you were suspicious about the OP's for they did not match the graph, you would have point this fact to him before giving adetailed answer.
And finally, what makes you so sure that the data you used after "eyeballed a few obvious points" are good: as you have probably noticed, the graph the OP gave does not mention the scales of the axis.
To end this, susceptibility is poor counselor.
You wrote "You seem to believe that the OP's selected points are important..." : NO, I just used your own words you used in your first answer "The overall strategy is to identify about six "important" points".
Please avoid rewritting the past