Some airlines without seniority lists have 'unofficial' lists - These are generally lists of people with their rank, and date of joining.
Many disputes such as base changes, fleet moves are settled by these 'unoffocial' lists.
Some also use alphabetical order for sorting out holiday, RDO's etc....may seem unfair, but they generally reverse it every year, so you may have been last this year, but first next! seems to work ok.
Redundancies are generally last in first out.