So, trying to get this straight. CD 13-16, there was no removal of the pessary, but you still observed fertile CM on toilet paper? That, in and of itself, would make me doubt that it is creating the kind of barrier that you're looking for. Then, you had a complete DTD on the morning of CD 14 and incomplete/withdrawn DTD's on the evenings of CD 13, 15, and 16? With a known DTD record in your fertile period, it sounds like it comes down to the effectiveness of the new pessary.
As far as rule-breaking is concerned, I'm not sure what set of rules exactly you were trying to follow. If you are talking about NFP with abstinence in the fertile period, then yes, that is rule-breaking. If you are talking about FAM with using other methods in the fertile period, then as long as you were using the pessary correctly, then it's not rule-breaking, though any failures would be related to failures in the pessary rather than in your ability to determine your fertile period. Technically, it would be a failure for both the pessary and FAM (since it allows barrier methods in the fertile period), but not for NFP. It would be too difficult to tell if there was a withdrawl failure or not because there was at least one complete DTD in the fertile period.
Feelings and decisions to be less cautious because you would be OK with getting pregnant also blur the line between unplanned and planned pregnancies difficult in many cases. It's not the "planned pregnancy" that everybody envisions where you go off birth control or switch from CTA to TTC and notate it in your chart ahead of time, joining the TTC forums, testing early and often, hoping that one of these months, you're going to get two lines. However, in some cases, depending on the circumstances, it's not necessarily an unplanned pregnancy either, where you are trying to avoid and doing your best to follow a contraceptive protocol, and something went wrong.