Luck of the draw in a glow plug failure of one plug in a year type of thing could also be a factor. The three cycles are perhaps not causing a lot of additional stress or just a little or maybe a lot. We probably lack this knowledge on site but the plug manufacturer might have the data. Failure of one plug in one cycle aplications after one year is not uncommon either.
If you locate and change the failure plug yourself no large financial outlay occurs. You are going to continue the three cycles most likely as a given if the car will not start otherwise.
When the weather warms up or you have a heated garage do a complete tuneup. It is time intensive rather than money. Valve adjustment, chain stretch, injection pump timing, etc.etc.
You know the manufacturer at the time of introduction wanted all these items looked at anyways about every thirty thousand miles. Some cars out there have far exceeded this milage it seems with nothing done if it still runs. As a bonus you may have more power as well. Not that you would particularily like or need it.
Symptoms like yours can be the result. There is no way of knowing unless you either know when they were done or do it. Can be many things causing your three cycle requirement. Some are easily addressable others are not.