Taylor Larimore, co-author of The Bogleheads Guide to Retirement Planning, on Wednesday acknowledged that his book contains errors in its discussions of stock investing risk.

He didn’t say the Three Magic Words. But he inched up closer to doing so than any long-time advocate of the Buy-and-Hold Model has done before (to my knowledge).

Taylor’s words came in a thread at the Bogleheads.org board entitled “The 50 Percent Fallacy.” A community member named “Tadamsmar” launched the thread, saying: “I wonder if there are any Bogleheads here who have made an attempt to square their philosophy of investment risk on the facts rather than on a fallacy?  If so, please speak up.”

Tadamsmar  noted that Page 142 of the Bogleheads Guide asserts that a 50 percent loss is the maximum loss that can be suffered by stock investors. This is of course a wildly false claim. The average loss on the three earlier occasions when stock prices went to double fair value is 68 percent real. On the one occasion when the P/E10 level went above 30, we saw a drop in stock prices of 80 percent real. In the late 1990s, the P/E10 level went to 44, far above what we have ever before seen in U.S. history.

Larimore responded defensively. He claimed that: ” Nowhere does the book say stocks (or any investment) can’t fall more than 50%.”

Numerous other defensive comments were posted. But some reasoned points were offered as well. “DBR” said: “Whether the Bogleheads book literally presents false information at that point is arguable. On re-reading, I can certainly see how a reader relying on no other sources of information could be mislead by the discussion presented there.”

After extensive discussion and obfuscation, Larmore acknowledged: “You are right. Figure 9.1 in the book should not use the words ‘Maximum Loss.’ Thank you for the correction.”

It’s a start. Eight years after we discovered the analytical errors in the Old School Safe Withdrawal Rate Studies, we have not heard any of the authors of the Old School studies or calculators make that clear an acknowledgement of their mistakes.

A few posts later, Taylor returned to Defensive Mode. He said: “Over two dozen Boglehead retirement and financial experts contributed their time and knowledge to our second Bogleheads’ Guide without renumeration. Like any book, it contains mistakes and some things may not be perfectly clear to every reader. Despite its shortcomings, customer reviews at Amazon give our book a 5-STAR rating and it is recommended by many reviewers, including Vanguard. Please tell us what you like about the book.”

Tadamsmar observed in response to one of the many defensive comments put forward by Boglehead.org community members that: “If I make a correct statement and people keep coming back and telling me I am wrong, then I guess this might continue forever.”

Taylor has claimed on earlier occasions that the reason why he favors a ban on posts pointing out the flaws in the Buy-and-Hold Model is that Buy-and-Hold is the only investing approach rooted in “science” and “academic research.”