Definitely some metrics won't easily compare to "feeling well slept" when sometimes it might seem to coincide nicely. For me, length of sleep and lining up that sleep with a good schedule, or misaligning them by having a late night or a short sleep, matches best. The scores can reflect that.
Another thing to consider altogether is that sleep cycles are a bit idiosyncratic. There is not an exact rhythm with an exact frequency, but we do tend to have light sleep, then deep sleep, some REM, then repeat.
I won't say I am certain as I am not an expert and not quite sure, I don't look at brain scans of myself sleeping, but I have read that when we wake up from light sleep cycle after getting decent deep and REM cycle, we might feel refreshed. On the other hand, if we wake during an REM cycle, our dreams will probably be more vivid to our short term memory. Yet again if we wake during a deep cycle or around a deep cycle, maybe we will have more fatigue as we wake.
Maybe, if multiple things happen in previous days, an awkward sleep cycle sequence could lead to lack of energy at day starts and through the days. In other words, the cause of waking sluggish may be connected to the daytime fatigue. There can be gradual trends through the weekly, monthly, and seasonal shifts, and so on.
