Basing off this image, it looks all but inevitable that During the HYW with France this will trip when, in reality, it didn't start until a few years after the end off the HYW.
assuming 2.50 gain per month, gives just 40 Months(3.3ish years), 2/month (assuming you raise stab right away) is 50 Months(4and a bit years); For the AI england, yes typically its "given" up at 15-18 mths, For the player though, this could be a major blow for the player while still fighting for the France throne.
My recommendation, would be to have a hard block flag with HYW going on, but increase the rate at when it does start to tick, to tick. Perhaps double the rates.