Did Wolvie invite Northstar to join up at the end of X-Men # 163? Here's the banter:
Northstar scoots up to Havok and announces, "The school's under attack! I've been crisscrossing the forest looking for--" Bobby interrupts, "Under attack?! Why aren't you there, helping?!" Jean-Paul responds, with his arms folded, "Why aren't you? At least I have an excuse. I am not officially on an 'X team.'" Logan approaches, "Well, you are now, Bud. We'll take anyone who's willing."
And not to spoil #164 but Jean-Paul certainly acts as a team member, not like an individual as he did starting out his appearance earlier in #163.
The issue synopsis from uncannyxmen.net reads, "Wolverine, Polaris and Nocturne converge with the five men and Logan tells Jean-Paul that he is back on the team, as they will take anyone who is willing."