None of the bulbous iris tend to naturalize well IME. They prefer quite dry soils during their dormant period (summer through early-mid winter), which is opposite of typical climate patterns for most of North America. Clumps tend to peter out after a few years.

And I think your garden speaker may have been confused :-) If happy, the bulbs spread by offsets, so if the original bulbs are planted at the correct depth (2 inches deep), the offsets should be also.

Even here, where Dutch iris are grow for the cut flower market, bulbs are planted fresh each fall.

Some Dutch iris are better at persisting than others (try the blue and the blue/bronze one), and they are fine over summer as long as they have good drainage. Supposedly they are not tasty to gophers.. but I have had them disappear faster in the open garden than in wire lined beds. It helps to divide them in Fall as they tend to form a clump of small bulbs around the original.

I. reticulata and its relatives is an annual like Hybrid Tulips here in 9/10 - its just not cold enough in Winter to simulate their native conditions - from Brian Mathew:

Iris reticulata and its relatives are mountain plants native to western Asia, and thus used to hard winters. I have seen reticulatas growing in areas of Turkey and Iran where the winter temperatures certainly dip regularly to -25°F, although normally with good snow cover. Winter hardiness is therefore not in question. The success or otherwise of these delightful spring bulbs lies more in the summer conditions, as the bulbs like to be dormant and almost dry from early summer through to the autumn, when root growth commences once more.