Hard to tell for sure, but my gut is that your wife was being intentionally sneaky here, OP. Your professed reason for the rule is to avoid excessive entanglement with other people, by restricting time spent together. I get the strict definition of no overnights is "back before the sun rises", so technically your wife didn't violate the denotative meaning of the rule. That being said, she was also a party to that agreement, and based on my experience with human behavior, I highly doubt she wasn't somewhat cognizant of the fact that you might reasonably interpret her conduct as violating the agreement. It would have been no trouble for her to send a quick clarifying text at some point during the date, but then she takes the risk of pissing her date off because she didn't talk things over with her spouse. That last point in particular seems way too convenient for all this to be accidental, but then again, it's possible that the practice of law has made me too cynical 🤷‍♂️

I get that you want to avoid appearing overly controlling, but in a world where you and your spouse agree to this (very common) boundary, you've already crossed the Rubicon. Here, the vagueness of the rule got you the worst of both worlds: you not only were a party to "controlling" wifey's sexual conduct, but also got the nut-shot of insecurity when she "violated" the rule, if in spirit only.

The lesson here is to discuss things in specific detail, even if you feel it might cause friction with your spouse. Instead of "no overnights", you folks might either (a) discuss return times with longer dates as they appear, or (b) set a rule that you folks are to be gone from a date by a certain time, with no exceptions.