I have done a similar analysis, with similar results, except that I use 64 as my earliest SS date, primarily because at that is the earliest age my SS + DW SS + my pension fully covers our planned living expenses, and our savings/investments become extra money to spend/build an estate from. From opensocialsecurity, the projected lifetime difference of taking it at 64 is around $100K less that the optimal strategy... which is not a lot to sway me strongly to delay to 70. Or, perhaps I should say, there would have to be additional reasons beyond this difference to make delaying until 70 a strong case in my situation.
Curious, did you used the default discount rate of 0.16% (current TIPS rate, per the author), or did you selected advanced options and change it?
I have found it makes a big difference. For example, in our case:
Comparing at age 65 to the optimal
3% discount: $5,000 difference (about 1%)
2% discount: $19,000 difference (about 2.4%)
1% discount: $42,000 difference (about 4.7%)
Default (0.16%): $68,000 difference (about 6.6%)
So, if our real rate of return over the rest of our (statistical) lives is 3% or greater, it just doesn't matter.
And, if it really is just 0.16%, that simply means the heirs inherit $68,000 less than they MIGHT have.
These analyses leave me with the feeling I am either measuring with a micrometer and cutting with an ax, or measuring with a yard stick and cutting with a laser.
Statistically, there is little difference. And, the unknown (and unknowable) will have the greatest weight on the outcome.