Curious.. second time this happened:
booked LX flights, with EB# attached from the very beginning (no change at check-in/gate or so) and the miles wont be credited automatically (waited 12 days).
Using the retrocredit form (and yes, thanks, no BP scanning) produced "system errors", but after reloading the mileage overview, the miles are there!
So what's this - do I have to "prepare" to always use retrocredit? Since the data is obivously there/available, why not credit within some days (or right after boarding..)?