In my experience, you are probably not covered, even if you’ve done everything you can to be. I would also advise checking every word your vet writes, as that unsolicited comment that everything is good with that pre-existing condition that may be related future bills will mean that you aren’t fully covered.

My cat had a heart murmur, this was disclosed and the additional premium was paid.
As far as we were aware the cat had had the heart murmur since birth, no advice had been sought, medication prescribed or treatment had been given for at least five years.
Despite the years of no change and non treatment, Many Pets decided because the vet had completed the usual checks (weight, teeth, heart rate), noted that the previously diagnosed heart murmur wasn’t any worse during a routine visit for my cats vaccinations, clock would be restarted, so they get of paying for treatment.
Unfortunately we lost my cat to heart failure, Many Pets decided that treatment required was directly related to the heart murmur (this is unproven and just their say so).
So not only have they decided that the heart failure was directly related to the heart murmur and therefore moving this treatment to pre-existing, but they also claim that these routine visits mean that two years haven’t passed and they don’t have to cover any more than a token amount.
So in my opinion they are actively selling a policy that they know in advance won’t cover the situation it was purchased for.
Maybe my vets are unusual, but no matter why any of my pets are taken in, they always complete the basic checks. According to Many Pets these basic checks (carried out as a matter of course on an annual basis) effectively null and void the pre-existing conditions benefits you pay for, by not allowing them to ever go two years without mention of a previous condition.

So if you are a responsible pet owner you are probably not covered.

I would also note that it takes an extremely long time for Many Pets to respond to a claim. In this case, that meant several thousand of pounds of additional uncovered treatment had been incurred.