It would indeed seem that Data was the only sentient android in existence in the TNG/DS9/VOY era. At least this is what Torres claims outright when the Pralor android interviews her in VOY "Prototype".
This of course skirts the issue of Lore and Julianna Tainer, two further Soongian androids that may or may not have existed at that time. But Torres might omit those for simplicity, or she might be aware that Lore was dismantled and that Julianna had recently died, or something. And she might dismiss any further Soongian creations as incomplete.
It may well be that the Federation still dabbles in androids in the 24th century, but sees no reason to give them sapience. Or it may be that the Federation eagerly toys with all sorts of artificial sapience, but sees no value in putting those in android bodies. Dr Soong seems to have been alone in his quest for android sapience - the leading Federation researcher Ira Graves rather dismisses Soong's flagship product, Data, in TNG "The Schitzoid Man".
The planet of androids might not count as a planet of sentient androids by the 24th century standards; the puppets there weren't all that sophisticated mentally, after all. Norman might have been the only really sentient android there, and he could be gone for good.
Alternately, the planet might never have become part of the Federation, nor even agreed to deal with it, which would lead Torres to exclude it from consideration.
Timo Saloniemi