She’s holding on to her 27.6 speed, such as it is, better this year over 400m than she held on to her 26.65 speed over 400m last year.
The same thing goes for the 60m speed over 200m.
That might mean better endurance, or it might just be because slower speed is easier to hang on to, or she might be pacing herself more this year over 400m. There’s raw speed, there’s endurance, and there are tactics, and the way the three interplay gives you your 200m and 400m times. There might be other things, but I’ll defer to the track guys on that.