Just a minor aside: beware that the DevAddr is not unique. I don’t know if KPN is doing any segmentation, but surely TTN is not randomly using all 25 bits it can use for its prefix as assigned by the LoRa Alliance. Instead, TTN probably only uses 2601xxxx and 260Bxxxx for its community network in the Netherlands. And (at least in V2) it then uses more segmentation to define specific classes:
Within a region, the NetworkServer is responsible for assigning device addresses. We are using prefixes here too for different device classes (for example, ABP devices in the
euregion start with0x26011) or to shard devices over different servers
If that still holds in V3, then TTN has about 2 × 1.5 bytes = 8,192 unique values for, say, an OTAA DevAddr in The Netherlands. So, some of the unique device addresses you have seen may be multiple devices.
See also Update on DevAddr Block Assignments on The Things Stack Community Edition clusters.