I'm not sure exactly where you're getting this information from. Cockfosters, Shepard's Bush and St. John's Wood* form the Triple Entendre set, which you claimed to enforce. Playing these three is a common gambit at tournament level, and I certainly know it won me the first price at the Coventry Regional Championship when I was a more active tournament player in '08. You cannot invoke an Endendre manoeuvre unless at least two of these stations have been played in close proximity. It's just not a debatable rule, here, it has been a part of the standard core of the rules since they bricked up Down Street in '39
** after the war.
* Some variants allow for an expanded number of stations to form an Entendre, including Monument and Arsenal.
** Sadly, this link doesn't talk about the game ramifications of the lost stations. Though it would be nice to try and play a lost station sub-rule set if anyone felt up to it.