As I understand it (because I had the same query and someone on the Zwift Forums tried to answer it for me) the results page only shows any increase in Racing Score based on results and NOT the increase you might get from having a higher power "seed". This means people who haven't raced in over 90 days can have artificially depressed racing scores enabling them to enter lower pens, which then jump back up to their normal values again after their first race.
Take your race winner - my guess is that they entered the race with a score of about 260, but because they set new 90-day power records, their score leapt up by 200 or so (not shown) plus another 8 from the race (shown). Not much you can do about it unfortunately.
Thanks - that explains it.
I had assumed that when the results show that the winner's ZRS has increased by 8 to 468 he had started the race on 460. Digging into ZwiftPower it looks like he started the race on 214 after a long layoff*. A massive 5 minute PB more than doubled his Racing Score.
The other people in the top couple of positions have similar, but not quite so dramatic, stories.
* I don't think that we can blame the layoff on his loss to Alex as this guy has a different name and nationality
