I guess we could argue that creating androids in the spitting image of Noonien Soong would be a common prank, one unlikely to be the work of the man himself.
I mean, the body of Data isn't evidence of the work of a genius: Ira Graves dismisses that bit as mere tinkertoy nonsense. What makes Data tick is what matters.
Which brings us to the two actual questions:
1) Is it common to have androids around passing the Turing test while tapdancing on a high wire blindfolded?
2) Can positronics be detected somehow?
On the first one, we have Torres' word that Data is the only one of his kind (that is, sentient android) known to exist in the early 2370s. That doesn't preclude others existing in the preceding decades or centuries, though, Androids don't exactly follow the "be fruitful and multiply" directive in Trek; instead, individuals are likely to live long and prosper, and perhaps tinker incessantly with offspring projects that never quite meet their satisfaction (see Flint and his endless series of experiments, too). Perhaps an android waltzing in isn't an uncommon occurrence at all, and instead is actually a fairly general trend? That is, immortal individuals of that sort might generally be rootless and pastless and prone to experiment with weird professions, and the UFP Foreign Legion aka Starfleet is happy to take them, few questions asked.
On the second one, we know B-4 leaked positronic telltale signals. Might be he leaked worse than Data or Lore or Tainer because he was an early model. Might be because the Romulans built him to leak like that so that they could better lure in a Starfleet sucker. But it's merely "leaked worse", not "leaked" - the heroes readily accept that positronic leakage is a characteristic of Soongian androids. Then again, nobody detected that Tainer leaked. Nobody noticed that Lore survived intact the beam-out at the end of "Datalore". It was in general difficult to locate Data across distances with a mere tricorder (unlike with B-4). That's three datapoints: is the last equal to the first two? That is, were Data's leaks also nigh-impossible to spot unless one knew exactly how to look?
It's worth noting that Soong wasn't the fool who claimed positronic androids could be made. He was the fool who claimed positronic computers in general could be made. Since nobody else ever made those before "Datalore", it might well be nobody would know what to look for in a potential positronic brain. Not even if and when they opened Data's skull, which had plenty of those convenient access hatches. Sure, Data was a bit secretive about his off switch. But being open about his openings would be an obvious survival strategy in the examinations that he must have been subjected to initially.
Timo Saloniemi
