Today's selection? This early 20th century McCall pattern:
How early? Well, that's a very interesting question. It gives a patent date on the back of the pattern, April 21, 1908 (no patent number, which would make it quick and easy to look up, but i'm not complaining...). However, that patent isn't for an individual pattern design, but for the "guide chart" system that keys the instructions to portions of the garment illustrations. Yep, that little bitty fine print on the back of the pattern envelope and those tiny little line drawings are all the instructions you get...
So we know at least that it's not earlier than April 21, 1908 - but how much later? This being a child's pattern, the sizes are given by age rather than measurement, and i know that's an indicator of an older pattern, but i don't know just when McCall switched to sizing them by measurement. A boy's shirt is also not the trendiest of garments, so the design of the garment only gives you a ballpark on this one. I have seen early 1920s McCall patterns that have a different, much more ornate envelope design, but don't know if that was used on their whole line, nor exactly when it came into use... more research!