Sometimes, being the bearer of bad news is necessary, although it’s not fun or nice to do.
On a regular basis, the PIC receives contacts from members who just found out, or realized, that they made a flight (or multiple flights) as PIC, after their most recent flight review had expired. The typical question is ‘what can I do to correct or fix that?’ The simple, honest answer here is nothing. You cannot change that. What’s done is done. The good news – it was unintentional. The bad news - you still violated the FAA regulation. And that bell cannot be un-rung.
If you have done this, don’t go broadcasting the fact, do get a flight review as your next flight, and set reminders so it doesn’t happen again. File a NASA ASRS report if you are so inclined.
Most are concerned that an instructor, an examiner, or FAA inspector will call them out on it, and that is possible if you already entered the flight in your logbook. If you haven’t entered it, then there is no “official” record of it. If you have entered it, a single strike through or obliteration of the entry is akin to a bullseye target and will draw attention. The best advice is to just leave it there and deal with any consequences down the road; be truthful.
AOPA's Pilot Information Center is available by phone M-F 8:30-6:00 ET, 800-872-2672, or via email at firstname.lastname@example.org
As an itinerant flight instructor training pilots all over the US (well, not Hawaii yet, but the other 49 are covered), I see logbooks like this from time to time. Of course, that's not a problem for us when conducting a 10-day instrument rating course, as I'm PIC for the training, and over 10 days of instrument training I can certainly get a flight review done and documented (including both appropriate remarks for the flight training and logging appropriate ground training, too). I've also found people flying a PA-32 without a High Performance endorsement, retractables without a complex endorsement, and turbocharged planes with service ceilings above 25,000 without a high altitude endorsement. Of course, these, too, can get fixed easily over a 10-day course.
The big problem would be if I signed their 8710-1 for the instrument test, and then the DPE had to stop the show before it started because s/he discovered what I had missed. Remember that on the practical test, the applicant, not the examiner, is the PIC, and must (except for the small exception about passenger carriage in 61.47(c)) meet all PIC requirements, including flight review (or equivalent, like WINGS), HP/complex/high altitude, etc. If the applicant doesn't meet those requirements, not only will the examiner refuse to do the test, the applicant will not be permitted to fly home from the test site. It's also going to make me look bad before that examiner for allowing it to happen, and a reputation for missing things isn't something I need – not good for my trainees, either, if the examiner starts thinking s/he needs to be extra careful with my trainees. That's why I'm careful to check all those things on the first day of training, Of course, as Daddis suggested, I'm not going to put anything to that logbook to draw attention to the problem, but I absolutely will make sure the trainee understands the issue and the potential consequences if caught by the FAA.
That said, it is, at the end of the day, it's every pilot's own responsibility to make sure they're legal to be the PIC for the flight, just as it's their responsibility to ensure the plane is legally airworthy (see 14 CFR 91.7).