One of the problems with the KLM website is that it is airline specific. In other words, although KLM is part of Sky Team, the KLM website only really gives you access to KLM. Try booking a Delta flight on KLM and then trying to get decent seats. The full seating plan simply isn't shown in the KLM site. For that reason, I book Delta's own website if flying on with them from a KLM start flight. It works better that way.
Similarly, it's usually impossible to satisfactorily complete a check in when in JNB returning to AMS. Seat plans for the actual flight thirty hours later just are not available.
KLM are perfectly well aware of these problems. I've telephoned them many times from all over the world and sometimes received MCOs as an apology for various intrusions into my own convenience. The link up with Air France hasn't helped. It would seem that AF is actually the dominant partner, or at least that's the KLM staff's excuse. The Air France website is more dangerous to navigate with a credit card than any airline site I know and Air France simply have no such thing as customer service. One of the reasons for that of course is that after the KLM/AF merge, AF got rid of most, if not all, KLM out station staff, reservations etc, outsourced everything and then stood back to await the time when lousy service would improve profits.