Can single strokes cause progressive dementia?

No: A single stroke might cause behavior changes or memory problems like dementia, but the changes would not be progressive. The confusing factor is that there is often associated "small vessel disease: this means prior tiny strokes involving the central part of the brain that may have been clinically silent. This picture can be associated with a progressive dementia.

Sometimes: Depends on location size type and cause.

A single stroke: Is not likely to cause a progressive dementia, but a series of single strokes can.

Stroke: Depends on site, extent and cause, and type of treatment provided.

Yes: A large enough single stroke can cause dementia. The underlying disease that caused the stroke can lead to further deficits and progressive dementia.