For classes of positions for which the department or a designated appointing power finds it difficult to maintain adequate eligible lists it may receive applications, conduct examinations, and create eligible lists continuously. The names of eligibles who took the same or a comparable examination on different dates may be ranked for purposes of certification in the order of final earned ratings, except as the order may be modified by the application of veterans preferences or career credits, consistent with applicable statutes. Eligibility from a continuous examination may be deemed to be established as of the date of examination.