I always forget to record the "sow on" date, or lose the scrap of paper where I wrote it down. Then I regret not knowing when I planted that particular crop, because I find out a few months later whether that date was too early, too late or just right.
Every plant variety has different cold and heat tolerances. Each bed may have a different exposure and a different micro-climate. Each year is also different, so records are the only way to capture the knowledge of the dates that are best for you.
The only way I can avoid losing my notes is to keep them always in the same place, such as one directory on my computer, or the paper gardening calendar that I never get around to creating.
During the winter, I like creating a Wish-List of varieties to grow that year. It gives me an excuse to fumble through my seed collection and daydream.
Printing out that wish-list with blank date columns for "direct sown," "emerged," "started indoors," and "planted out" will give you a head start toward record-keeping. Follow up with notes, such as "too early - killed by frost" or "next year, try it three weeks earlier to avoid summer heat." With notes that don't get lost, eventually you'll find the dates when each variety is most tender, flavorful, productive, or pest-resistant.
In addition to helping perfect your starting dates, recording where each variety went and what it was is also handy, unless your memory is ten times better than mine.
Plant tags get buried in foliage or lost, but a small blank map of your beds can be drawn and Xeroxed once, then used for many sowings over many years. Successive sowings could have a separate date on each row.
I have tried to rely on my non-existent artistic talent by hand-drawing maps. That was just embarrassing. So I tried making a map in Visio / AutoCAD. The proportions may still be wrong, but at least the labels tell me what-is-where after the plant tags get lost.