Regarding the address, it wasn't wholly ficticious. Even if someone in the Chess club had said categorically "There's no Menlove Gardens East, but there are other Menlove Gardens.", there was a strong chance Wallace would have still gone, on the reasonable assumption that Beattie had simply misheard the message, and Qualtrough would be found at West, North or South. Wallace had no doubt had similar experiences in the past in his long career as a door-to-door collector, and, given what we know about his character, may even have been determined to "get to the bottom" of the mysterious call.

Also, Menlove Gardens had only just been built and other streets were in the process of construction, so an element of fuzziness in the address would not automatically arouse suspicion.

And if Wallace was being stalked, as seems likely, there was no great downside. The culprits would know he hadn't taken the bait, and if he hadn't taken it, we wouldn't be discussing it here now!