I kept a spreadsheet tray map of my seedlings for many years, but several times got them mixed up by rearranging (due to height differences under the lights) or dropping the tray. Now I just jot a letter or two on the individual plastic pots with a sharpie and I can move them around all I want without worry. Each year I cross off the old letters and reuse the pots.
TomNJ/VA
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