The rewards you got from the Library Pass is what you were missing.
It is not the total x3 rewards all over again, as you have already collected a portion of those rewards when the Pass was purchased - excluding some of the rewards that were fully not given at the time.
For example; if you collected 100 Gold and bought the Pass and got given an additional 50 Gold, the mail you would have received would be 150 Gold and not 300 Gold.
Additionally, at the time 9.1 launched, players were rewarded the 150 Star Stones from the tutorial and in the initial broken Library Pass rewards were given an extra 100 (total 250) instead of being rewarded a total 450.
Now that has been mailed out, you would have received +200 Star Stones.