Thank you for your explanation Alan!
Since I started this hobby in the early 1980's with monitoring ACARS, DLH was changing there flightnumbers every new season. Still I do not understand why they do so and why they do not make there flightid's public. It is a big mysterie and big job to find out every timetable-change...
Thank you again and keep up the good work please!
Kind Regards, John