I have seen both here in Spain, and the criteria is unclear, as every operator is different, and even an operator has a different criteria depending on the site.
They seem to agree in an antenna migration to be able to allocate new frequencies. Most of the 3G is being migrated to mixed mode 3g/4g.
What we see here mostly is NSA. IOT cells I have seen so far are B20, defined on some LTE basebands.
So the old antennas are being migrated to be able to allocate mixed frequencies on a baseband system, and they add active antennas probably aiming at 5G SA, even if it’s NSA actually.