Difference in barcode/QR-code on eID

[Iris]

We are developing an in-house webapp and would need the serial-number of the eID. We noticed a difference between the 'old' eIDs and the european model in the barcode/QR-code.

When scanning the barcode (older eIDs) all information is shown in 1 string and the first 3 numbers of the serial number are missing. The QR-code (european model) shows comma-separated data and the full serial number.

Why is there a difference? Are the 3 first numbers of the 'old eID' always the same?

Is there another way to get the eID serial-number without a specific middleware?