Good to know they are working well for you.
Once upon a time I had a DPA published table which showed the mic performance changes of the 406x series at various less than specified nominal supply voltages. I looked but can't find it in my files, and an online search didn't turn it up either. I think I posted it in a 406x thread here at TS at some point, but could be mistaken. The basic jist was pretty much as expected- As supply voltage drops below the nominal down, self noise rises, max SPL drops, distortion thresholds drop, and peak output voltage drops. Obviously at some point the mic stops working entirely. The take away is that the mic may still work when powered with a lower than it's nominal supply voltage, but is likely to be doing so with reduced performance, and to a greater and greater degree as the supply voltage drops further.
In other words, even though they are specified as requiring 5V, some 4060 or 4061 examples may still function when supplied with the low 2.5-3V PIP provided by handheld recorders. But even if they work, they are likely to not be performing to specification, manifesting primarily as increased noise and distortion. Where as 4063 in the same situation is likely to perform closer to spec.