"Applicants must have at least 12 months of full-time, Canadian skilled work experience (or the equivalent in part-time work experience) in one or more NOC 0, A or B occupations within the 36 months before the date of application receipt [R87.1(2)(a)]."
Yes, you can combine different jobs with different (skilled) NOCs to qualify for CEC. Not that it is an issue for you, but you would have to meet the minimum language test scores for the NOC with the most experience (under the CEC program, minimum scores are lower for NOC B than for NOC A &O). With the same amount of work experience, you would (probably) have to meet the language level requirements for NOC A.