My dad is in an on-again-off-again relationship with a woman I've met a couple times. I am unable to call my dad right now or anytime soon (he's out of the country). They don't "officially" live together when they're together (I don't think). We don't have inner envelopes.
Would it be okay to address the outer envelope to just my dad and on the RSVP card "we have reserved 2 seats in your honour"?
I don't want to exclude the possible/probable girlfriend, but I highly doubt she'd be offended and I could see my dad raising an eyebrow at the envelope if her name was on it, or even thinking I was weird if I did ask him (strange relationship the two of us).
What's the official rule (pretty sure it would be to include her name IF they're dating the day the invites go out -- but it's tricky to find that out)?
Do the circumstances give me any leeway?

Thanks!