Minor mistakes usually do not cause a problem. Failure to list all countries visited, so long as those trips were otherwise in a period of time declared to be abroad, should be considered a minor mistake of little or no import.
Of course a problem can arise if and when CIC does a comparison of declared travel and stamps in the passport, and notices the discrepancy (no declaration as to entry or exit for the respective country reflected in the passport stamp). But it should be readily recognized that the stamps are dated within a period of time declared abroad and thus should still not cause much of a problem.
If there are other things causing CIC to have concerns, however, then sure, any and all mistakes will contribute to how negatively CIC views things. Any mistake shows the individual's failure to be an entirely accurate reporter of facts, so if there are other problems suggesting, to CIC, compromised credibility, then the little mistakes can become part of that overall picture, one of an individual whose credibility is compromised.
As for the passport pages: they do not show everything and are not relied upon to be complete proof of all travel . . . not by a long shot. When CIC requests the whole passport, the failure to submit it can be a huge problem, but submitting the passport does not necessarily satisfy CIC if CIC has questions. Whether CIC has questions or issues depends on the particular facts of the specific PR's case. If there are questions, if CIC pursues a Residency Determination, proof of place of abode and place of employment in Canada, among other evidence, can be required.
