Interesting.
The Sorcery (Grimoire) skill allows you access to all the spells in the grimoire, and the skill description says that your character can memorise as many spells as the grimoire holds, subject to the INT limit.
It doesn't say how many spells you get at the start of play.
This looks like something to thrash out between you and the GM. The GM will need to come up with specific grimoires and the spells each contains anyhow - but subject to the INT limit, if your character has two grimoires, one with five spells, one with eight spells, and he has an INT score of 17, he could theoretically start play with thirteen different sorcery spells and still have four INT slots free for another grimoire. If he then picks up a third grimoire containing six spells, he'll only have room for four of those spells from the third grimoire.
It would seem that you only have two restrictions, then: the whims of the GM and the character's INT score.