Thank you for the replies!
The reason for not choosing the Swiss flight were, that it was not possible to reach as it had an earlier departure then KL672.
When I called KLM because I was not able to check in online. There were about four and a half hours to departure
Had KLM proactively informed me of KL672's cancelation when it happened some 2 weeks earlier I would of course had chosen Swiss, for double dip reasons.
In regards to the ticket numbers, I thought of guessed so. It just looked weird that they changed a ticket number that had already been changed and flown.