I have Petplan insurance. I looked at a lot of other insurance plans before deciding on Petplan, mainly because of okay customer reviews. (I am suspicious of too-glowing and too-negative reviews. Some reviews are "plants".) I have been very pleased with Petplan. Ritz has stress-induced UTIs, which first occurred about nine months after I first enrolled. Amount of reimbursement paid for the yearly premium. Petplan for services I didn't expect it to pay, like expressing anal glands, clipping nails and Pill Pockets. I will renew in May and am thinking about upgrading my coverage to including boarding fees.
When I was doing my research, I found what you, Alley Cat, found: if the condition is 'pre-existing', then coverage is excluded; and like Carolina also stated, once deemed "cured"--sometimes for a stated period of time, usually 6 months to one year--the condition is no longer a preexisting illness. BUT READ FINE PRINT: In Petplan's fine print, a preexisting illness is a "condition which first occurred or showed clinical signs before the effective date of this policy or which occurred during the policy waiting period."
I also found that you can get several 'levels' of coverage within one plan. Levels vary from company to company. You might search for companies that cover pre-existing conditions; you'll pay a higher premium, of course, but may be worth it in the end.