If you wash yeast, then you certainly have the know and skill to make a simple starter. This makes sure you have viable yeast and also vastly increases the cell counts. With washed yeast, especially older than a few weeks, a starter is a great idea. I make a starter for all of my washed yeast and I have had great success. I capture fairly small washed samples, but lots of them. I just make starters and step them up as necassary. I find that I would rather have many small samples of yeast to use over time than use up my entire strain pitching big slurries without starters.