Not sure if this is the right place or if there is already a thread for it, but I couldn't find it. So moderators, feel free to move if you think it's appropriate.

First off, I am not looking for advice, as "it's gonna be fine", I am sure. It is just for your amusement. It spans two airlines and their IT systems, but I am posting it here since Delta are who issued my tickets.

I will be on a flight from Europe to the US soon, sold and mostly operated by Delta, with the first leg being a KLM codeshare. When I booked the flight, the TATL segment was in PS, so Delta told me that I can check 2 bags, weighing up to 23 kg/50 lbs each. Makes sense. Loading the trip in the KLM app, it shows only 1 checked bag included, with the same weight limits applying. I contacted their support, and they told me the app is wrong, and what Delta says is right. Okay. I also paid a bit of an upcharge on KLM to get an extra legroom seat. It's just a short hop, but the start of a VERY long journey, so I went for that route. Payment went through, I selected a seat. All seemed well.

Now cam the time to check in online (with KLM, as they operate the first leg). Weird thing number one is that I was not able (and still am not able) to check the seat map for the first leg and potentially move to a better seat. Initially, they blocked the first 6 rows for "business class" (which doesn't mean much on an E190 anyway), and I was right behind this. Hoping that the divider has been moved forward in the meantime, I wanted to check.. no "Can't do it, a payment is pending." What the heck? Well, shrug it off, go through the check-in, present all information needed, check-in successful. Trying to load the boarding passes in the KLM app, they didn't show up, telling me I need to go to the check-in desk at the airport. "Oh no, it's time for SSSS again", I thought, as this was the reason why I couldn't get my boarding pass online last time.

So I checked the KLM website. "Here's the PDF with your boarding passes, bro." No SSSS. Phew.
I checked the Delta website. "Here's the PDF with your boarding passes, bro." No SSSS either. Phew.
After waiting for the official check-in window to open on Delta (KLM gives you 30 instead of 24 hours), the Delta app also showed my boarding passes, no SSSS. For a strange reason, I can't save them to my Google wallet, but who cares. KLM App still refuses to load them.

Confusion doesn't end there. Remember the KLM app saying 1 bag, 23 kg/50 lbs, while Delta said two of them? The KLM website now says 3(!) bags, 32 kg/70 lbs each. Delta disagrees with that - at least their website and app agree on 2 pieces, 32 kg/70 lbs each. In practice, it doesn't make too much of a difference, as I usually do check 2 bags if I can (for redundancy in case one travels around the world without me), but the combined weight of them is less than 50 lbs.

My work for the most part is telling computers how to do things. Seriously, if we handed something like that to our customers, we would be out of business in no time. After working together for so much time, I would have expected that they got their stuff straight by now. But apparently, that is not the case.

The KLM system still doesn't know how to deal with Delta PS fares, and DL books into what is essentially a non-existant fare class (P/A/G) on the KLM codeshare intra-EU flights. But, it should've given you access to the 'economy comfort' seats without having to pay more. This also causes issues with using GUCs.

I was never able to get any seat except for the regular ones in the back of the bus on that KLM segment without having to pay. It's not the first time I am taking this trip. No matter if I try via Delta or KLM (and right now neither works).

There is no great forum for this� I HATE trying to work through the AF/KL/DL platforms for routes like this.

Anytime multiple airlines, partners, codeshares, etc get involved it can get very messy very fast. Usually if I'm traveling on a partner operated flight I just assume the app won't work and it'll be a paper BP day. I would love to see everything get streamlined and truly seamless, but it's far from it.

I'll never forget my first time transiting ICN connecting to KE. I approached the gate agent in ICN to ask a question, who's reply was "sometimes Delta tickets no work here." My confidence was really boosted that day haha.

I prefer to have a printout of my boarding pass anyway. Sure, there should be a charging port at my seat on the plane. But if it doesn't work and my phone runs out of battery, I still prefer to have the paper.

It's my (I think) fourth time to take exactly this trip with the same routing and the same airlines involved, and it used to work without any problems in the past. Even when you had to submit a lot more paperwork before traveling to the US (proof of Covid vaccination and all that jazz).
Another funny detail is that, while the boarding pass for my first leg to Amsterdam doesn't say "TSA Precheck", both the segment out of Amsterdam and the connection in the US say it. What is so funny about it is that a) there is no TSA and thus no precheck line in AMS, and I don't even have to pass through security there anyway. Only after entering the US, they want to go through my stuff...

Same issue with Air France. Am on a PS ticket bought through DL and the return is all operated by Air France and for that intra-European segment, the Air France website and the DL app are making me pay for any of their 'Prefered Seats' despite even having Sky Team Elite Status . I guess I should just be grateful that the baggage allowance is showing 3 bags as it should be .

To sum it up:
I got the seat that I paid for, the check-in agent also saw a message about a pending payment and didn't know what to make of that. I was able to check 2 bags, no problem (except for the fact that a 90 min delay into AMS meant that my 2-hour connection was down to 30 minutes, which I just about made, but my bags didn't).
Never got the KLM boarding passes to work in the app, but I used the printouts and what was in my Fly Delta App, and never had an issue anywhere.

Any flight to/from US has information submitted to TSA. Thus Precheck will appear on the BP. As notes means nothing to the US. Heck even with Precheck, you can still be SSSS selected.