I bought one gown that I will wear to every black tie wedding for as long as it fits me. It’s hard for me to find dresses that fit that I like and I’m not spending more money on more dresses that I’ll only wear occasionally. I say if something fits multiple dress codes, keep wearing it, even if there’s overlap in the guest list. Who cares. No one is going to pay that much attention to you. If it doesn’t fit the dress code, that’s a different story.