The intention is that the actual exposure should be exactly the same for equivalent exposure settings, but there are small deviations. There are also some other differences to the images other than the obvious (e.g. different depth of focus for different apertures).
Here are some differences that you may experience when choosing a different setting with the equivalent exposure:
Theoretically, the exposure would be exactly the same. In practice, the measurements are not exactly accurate. The f/8 might be f/7.9, the ISO 200 might be ISO 190. Those small differences keeps the exposure from being exactly the same.
However, the differences tend to be consistent, so if ISO 200 is actually ISO 190, then ISO 400 would be around ISO 380. That makes the difference in exposure between settings smaller than the actual inaccuracies of the measurements.
With different apertures you can get a focus shift, i.e. the focus plane can be at different places depending on the aperture. This is mostly only noticable for lenses with apertures f/1.4 and larger.
At small apertures, smaller than the diffraction limited aperture for a specific camera, the diffraction affects the image, which will make the images less sharp.
All kinds of distorsions, like perspective distorsion, vignetting, edge sharpness, general sharpness, will be more or less apparent at different apertures.
With very long exposure times (several minutes) the components in the camera heat up and can cause extra noise.
With different ISO settings you get different amount of noise.