@CherineAmr and
@Pasar86
As the previous discussion emphasized, the main thing is whether or not the applicant still meets the minimum physical presence requirement AFTER deducting any known absences not included with the applicant's initial presence calculation. There is no discretion to grant citizenship if the applicant fails to prove AT LEAST 1095 days of actual presence during the five year eligibility period.
Thus, the main effect of overlooking a trip or more abroad, or otherwise making a mistake that reduces the credit for days present in Canada,
DEPENDS on whether the number of days involved is more than the margin above the minimum the applicant had in the initial application. For example, applicants have reported failing to report weeks abroad, but they applied with a large enough margin over the minimum they still met the requirement . . . some proceeded soon to take the oath, no problems, no delays. Others report they needed to submit more information or evidence so that IRCC could verify they were sufficiently present in Canada to meet the requirements.
The latter leads to the credibility question.
In particular, beyond the direct impact of recalculating the number of days given recognized omissions, the impact is largely a matter of credibility depending on the nature, scope, and number of errors. IRCC is well aware that people make mistakes, and in most cases IRCC does NOT punish applicants for minor, unintentional mistakes. But obviously, mistakes reveal the applicant was not entirely an accurate reporter of facts, so any significant error can result in compromising the applicant's credibility no matter how innocent the mistake. The more and bigger the discrepancies, the more IRCC MUST doubt the applicant's information about time in Canada versus time outside Canada.
And of course the two are related. The smaller the margin over the minimum, the more scrutiny IRCC is likely to employ in response to mistakes, the more IRCC may make requests for additional documents . . . ranging from requesting this or that particular document, up to issuing the applicant the full blown Residency Questionnaire. This makes total sense. For an applicant who applied with two hundred or more days extra, above the minimum, if IRCC identifies or suspects the applicant missed a few days here or there but does not otherwise doubt the applicant's information, it is easy for IRCC to proceed with a decision granting citizenship. Despite some mistakes it is obvious the applicant met the requirements.
In contrast, if the applicant applied with a rather small margin over the minimum, such as just thirty or forty extra days, and IRCC apprehends there may have been a week or three more abroad than reported, that brings the applicant a lot closer to falling short . . . and thus puts a lot more pressure on IRCC to FOR-SURE verify the applicant met the minimum presence requirement.
Which leads to applicants who applied with virtually no margin (not sure why, but there seems to be more than a few who do this), less than ten days extra. Obviously, if IRCC discerns such an applicant made mistakes, that puts a lot of pressure on IRCC to get verification. Again, IRCC has NO DISCRETION to grant citizenship if the applicant falls even ONE DAY short.
Overall the impact of small or few errors is usually NOT a problem . . . unless the applicant had little or no margin over the minimum. Worst case scenario, usually, is the applicant will be asked to provide additional information and documents to help IRCC better verify the applicant's presence. Beyond that, how it goes depends on the extent to which the mistakes raise questions about the applicant's ability to be an accurate reporter (that is, the applicant's credibility), ranging from having little impact on how IRCC perceives the applicant's credibility, to the more egregious scenarios in which IRCC might suspect intentional misrepresentation (fraud).
So it matters whether
-- the interviewer has the impression the applicant is honest but just made a minor, unintentional mistake or two, or
-- the interviewer apprehends the applicant made significant mistakes and, perhaps, generally did not make an effort to get the information right and cannot be relied on beyond what is corroborated by objective information (such as the CBSA Travel History), or
-- the interviewer suspects the applicant was not honest
There are many other factors which can influence what IRCC officials perceive about the applicant.
Ultimately it is the applicant's burden to PROVE to IRCC's satisfaction that the applicant met the requirements. If IRCC is not satisfied by what the applicant submits, then the case will be referred to a Citizenship Judge to weigh the facts and evidence, and interview the applicant so as to directly judge the applicant's credibility.