For what? These often depend on the firm. Normally the number of years has little to do with level of responsibility, it’s the level of experience and responsibility your employer feels comfortable giving you.
Designer: everyone that does not have a license to practice (this goes whether you have 0 yrs or you are a 40yr veteran but are unlicensed).
LA: once you’re licensed you can call yourself a landscape architect legally.
Assuming this is a question for jobs at corporate offices: landscape designer is typically someone with little experience (0~5yrs) that can handle illustrative and construction drawings, general design and product selection with supervision; LAI is someone with limited experience (2~5yrs) but licensed similar to above but also probably includes limited coordination with consultants and more construction administrative work; LAII (3~10yrs) more project management and coordination. My resources are from seeing peers in corporate offices and understanding what they do – in a small/midsize office these tasks are generally shared by everyone until they become more involved in management .
If someone is a quick learner, team player, a good leader, and gets exposed to all phases of the work from proposal writing to construction administration, you typically move up the ladder faster. Other than that its a way to ‘recognize’ the growth of an individual and presumably some level of pay differential.
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