This still has acceptably useful information
https://web.archive.org/web/20191122024906/http://wiki.goallineblitz.com/index.php/Boosting"Once you have boosted your player 25 times, you receive an additional 20 Skill Points to spend on that player."
So it's that first boost of that 8th season. Picking a level is tricky because some people boost for VPs instead of XPs so they might be behind. 71 is a weird ass number.
At age 240 you're usually L68. Then you time your boost to get some leftover XP to exchange. So you're most likely looking at a dot that coasted from 68 to 71 and the XP shut down. So the first boost will get you +20 SPs.