PERSONAL BEST is not the same thing as SEASONS BEST. I believe you mean SEASONS BEST, not PERSONAL BEST.
PERSONAL BEST is the highest score a skater has received to date in a category (SP, FS, Total). It could have been achieved yesterday or 5 years ago.
For example, Nathan Chen's PERSONAL BEST SP is the 101.94 he got at Worlds 2018.
SEASONS BEST is the highest score achieved in a category in the current season.
Seasons Best scores can be reliable for skaters who are very consistent. Uno and Chen are quite consistent---their scores may vary a bit from one event to another, but remain in a high range, as you would expect from the World gold and silver medalists. Voronov's score was relatively low at SA but rose at NHK, which is usual for him---he usually does better as the season goes on. I'd expect him to be better at the GPF than he was at his two events.
Cha's score went down from SC to FIN, but then he had those two events back-to-back, and as he trains in Canada, he won't be traveling for the GPF. Brezina is unpredictable, but the judges love him and he always gets extremely high PCS. His performances have improved dramatically since the coaching change to Aratunian.
When Keegan is good, he can be very, very good. But when he is a little off, you don't know what you're going to get. I remember him well when he skated for the US---he could bring the house down, or he could lay an egg, and you never knew what he'd do until he took the ice.