Hello,
In reality, it is possible to see such errors. In the picture below, a clock signal (source) is being used to measure the period of the gate signal.
If any of the rising edges of the source line up with the rising edges of the gate, then it is possible that the count will be slightly inaccurate and be a source of error for the result.
The magnitude of this error would depend on the frequency of your signal. What is it?
Also this possible max error will vary based on your source signal.
Period Measurement with a Counter
Kameralina