In fact, theoretically, runners never reach 100% of their potentials at their respective careers. Some get very close to it of course, but it is hard to imagine a runner that had the following combination:
- being at the absolute prime of their fitness
- having a time trial race set up
- waking up on that day in the perfect mental state to break the record
- following a perfect pace maker for over half the distance
- perfect weather, perfect track, perfect everything
that is a theoretical race where we can say yes that runner achieved an optimal race and time.
Coe's 1:41.73 had a lot of those conditions but even at that race maybe the track could be better, pacing could've been slightly better, so yes, maybe in a 100% optimal race he could've run even a bit faster. Cruz 1:41.77 was also one of those races where lots of those conditions are met and he has run very close to the potential he had.
Of course some runners get a lot closer than others in regards to what they were truly capable, this is just reality.