This is in regards to an KL-issued, all DL-operated economy ticket C2-C1 rt. The outbound was completed without any issues (except the not being able to show up on any UG lists).
Now, the inbound (end of June) LGA-DTW-X was affected by a cancellation of LGA-DTW. Rebooked to LGA-ATL-X the next day; accidentally then rebooked for another day later JFK-AMS/CDG-X (all via the DL app/website). Eventually texting with DL and got them to reissue travel for LGA-DTW-MUC this Thursday. It involved the chat agent both reaching out to the global ticketing desk and them calling in KL since it was originally issued on KL. So kudos to the DL agents for actually figuring this out.

Now, the (still) all-DL itinerary is KL-marketed but on a DL-stock. And from some discussion with phone agents this seems to throw off the Delta IT somewhat. Eventually, they were (supposedly) able to select/request seats for me and told me that the DL PNR would not be able to reflect those but gave me a KL PNR that was showing them as requested.
Fast forward, checking this weekend, the seat map showed my "selected" seats as free/open. DL agents claimed that "KLM restricts seat assignment until 36 hrs before departure", which on an all-DL operated itinerary seems bogus.

I have also three issued ticket numbers, two KL and one DL. Looking the PNR up on pnr.sh the 006 one seems to be the one holding only two coupons matching the travel LGA-DTW-MUC.

I am fully expecting and have already 50% made my peace with not having a seat assigned and being stuck in a middle seat on the 764 on the l/h and will try and figure it out early at LGA. But does anyone have some intel or suggestions at what might be going on?

Cheers!