You get points stored not for unlocking some crystal, but for earning some points on top of the last crystal you've unlocked (not more than your spire archive capacity in total).

for example if your spire archive has 250 points capacity and already have 150 points stored at the end of the spire with 1000 points - you have two options:

1. get 100 more points into your archive (1000-880=120, but 150+120 is more than 250 that can be stored - so 20 would be wasted).

2. invest 80 points from archive and get next crystal (1080), leaving only 70 points in the archive.

If someone go further after that and earn, for example, 21 points (finishing spire with 1111 points overall) - you will get back those 21 points into archive and have 91 for the next week.