Books #1 and 2 First Edition Points

This five volume series was first introduced in 1912 with a two volume breeder set. The first edition dust jackets for the first two titles that were published in 1912 list only the two Young Engineer Series books:

The Young Engineers in Colorado
The Young Engineers in Arizona

But this jacket does not absolutely indicate a first edition. Determining the true first edition for the first two titles requires an analysis of the advertisements in the back. The true first edition lists only three Automobile Girl books whereas the later books list four Automobile Girl books.

Also the ad for the Young Engineers is different. The first edition blurb is the same as the dust jacket blurb.
The first edition-second state blurb is different. It is the one that is used in all subsequent Young Engineer ads.