FI's company party is in January, and the invitation says "formal attire." It doesn't mention "black tie" or anything like that just "formal attire." It also states the theme is the Oscars and that we should "dress like you're attending the Oscars."
With a little bit of Google image search, that appears to be mostly tuxes or nice suits for men and long dresses for women. However, last year's company party was held at an equally nice venue, and most men wore suits or a dress shirt & tie and most women had cocktail dresses.
Based on last year's experience, I purchased this dress before we received the invitation:
Do you think this is appropriate? FI doesn't own a suit, so he'll probably go with the black dress shirt and tie again. I don't want to be the underdressed couple, but I just can't imagine a company party where most people would have tuxes and evening gowns. This is a place where everyone wears jeans to work.
P.S. I figured the etiquette crowd would give me better responses than attire & accessories, since they seem very wedding-focused.