You didn't mention the capacity of the card you are using, the brand, and where you bought it from.
I don't think using a microSD to SD adapter is anything to be concerned about. I have been doing it for years with no issues.
However, there have been tons of fake SD and microSD cards on the market in recent years. The fake cards are not just counterfeit in terms of brand, but actually don't have the capacity they claim. The SD controller pretends that the card is a 128GB for example, when the real capacity may only be 8GB. Since you are using a K200D, it only support SDHC cards, which means you can only use a card up to 32GB. Larger cards will not work. So, the good news is that you are less likely to have a fake card. Those are generally of higher pretend capacity.
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HappyBison.com: tech, research and bison
Unfortunately, if you have a fake card, your data will really be gone. And the symptoms are similar to what you describe - the card seems to work at first, but then when you fill it up - by taking more pictures, it becomes corrupt, and the camera (or PC) can no longer read it correctly.
I now run h2testw on any storage media that I purchase - be it an SD card, USB flash drive, hard drive or SSD, so that I know before the return period is up if the device has the capacity advertised.