I found this to be an issue also (the multiple parts, multiple dates, how to keep track). I think you really need to commit to replacing them at same time, and using them for same length. I wasn’t comfortable writing on pieces with marker (also will likely wear off with frequent washing/sterilizing), and thought an engraver would create grooves for bugs to attach, kinda counter productive. I now am in the habit of making sure my nebulizer and Aerobika have been sterilized within 24 hours of use, which practically means I use only one set (I do AC once a day). I wash and sterilize after every use, so I replace my nebulizer every 3 months, and Aerobika every 6 months, due to concern frequent sterilization will degrade plastic a bit sooner.