.... Instead of...
"Your demand letter dated 12/14/2007 was received today. I do not recognize this debt as mine. Validate."
I think the reasonable, common sense approach is...
"I have been out of town for the last 6 weeks and just received your demand letter. I request validation per FDCPA (blah blah blah)"
The generic "six weeks" lacks the specificity that the date certain provides. The point is to put on the contemporaneous record the date that the alleged debtor believes the 30 day clock begins. By doing this it provides rebuttal a priori
to a possible common mailbox rule contention. The date certain is key. A further explaination is nice, but not really necessary.
As for your reliance on Mahon, remember the case was about the granting of summary judgment, not on the merits of the term "receipt".
Mahon did not, through evidence, rebut the presumption permitted by the common mailbox rule, and, quite rightly, lost on the summary judgment ruling because there was no contradictory fact. The Court merely explained the mechanism of the common mailbox rule and its legitimate presumption in the absence of factual rebuttal.
Would the Court have ruled as it did if there were factual rebuttal? Maybe, maybe not. But that was not the issue in Mahon, so it is an error to say that it was addressed.
One thing I think would have happened, though, is that the summary judgment would have been reversed, and the case sent back to the trier of fact since there were disputed facts.
A point that all need to understand while engaged in litigation, the law is what the Judge says it is on any given day. If you disagree, you have the right of appeal.