Sorry it took so long to reply to your post!

I was looking through the Burpee Catalog pages I scanned (for you, I think) a few years ago, and was able to narrow a few intro dates down:

Two separate varieties of Giant Imperial larkspurs - Gloria and Peach Blossom - are listed on page 62 of the 1933 Burpee catalog, so the strain was probably introduced before 1940.

Unwins Dwarf Dahlias are featured on a color plae in the 1934 Burpee catalog as one of "Six of the Finest Flowers Recently Introduced."

A color illustration of Centaurea "Blue Boy" is included in the 1940 Burpee Catalog - I didn't scan the page with its description.

Since I only scanned the pages that included zinnias, marigolds, and maybe asters, I think I will need to dig out my old catalogs and do some more research. I'll bet I can find a few more of the varieties on your list.

Thanks, Cecilia,
Any further info will be much appreciated. Regarding the Giant Imperial Larkspur, I have been led to believe that Blue Bell (1934) and Exquisite Pink (1929?) and White King (1937) were other separate colors, also White Spire (1930?), so I've wondered whether most trace back to the 1930's or earlier. Some of the old colors seem to be listed by some as in the "Exquisite" series, so that is a little confusing. I have a list of 19 colors in the series, not including Gloria and Peach Blossom.

I found a few earlier dates to add to the list (all from my Burpee catalog collection):

Calendula Pacific Beauty - 1954
Centaurea Blue Boy & Red Boy - 1940
Salvia Bonfire - 1930

The 1952 Burpee catalog lists Nicotiana Sensation; the 1953 one lists one named Daylight in addition to Sensation. I'm not sure if this "Daylight" is the same as "Daylight Sensation."

The 1952 catalog also includes a Scabiosa Giant Imperial Hybrids mix - I assume this is the same as Imperial Giants.

I'll check on the single-color larkspur varieties you mentioned tonight. Some of them sound familiar.

Turns out that the Burpee website includes a gallery of their old catalog art. Some of the years aren't well represented, but a couple of them are helpful:

The inside page 1 art from the 1914 catalog includes a drawing of "Crego's Giant Pink Aster," and a 1915 catalog page shows "three superb Crego asters" - pink, azure blue, and white.
Wouldn't it be great if some of the other old seed houses would post old catalog art on their websites?

Here is a link that might be useful: 1914 Burpee Art

Thanks for the additional info regarding dates for the calendula, centaureas and salvia. I'm growing Bonfire this year for the first time, but also another new tall one from Parks this year for comparison. I'd always assumed that Bonfire was too late for our climate, but decided to test it out. I know there are earlier strains of it, but it seems they are vanishing or are already gone. Its nice to be able to backdate the Crego asters another ten years.

I really appreciate you alerting me to the Burpee Art link - I very much enjoyed seeing the old covers. There are even a few intro dates given on some of them, although don't think it was for anything that I was looking for - mostly items I never knew existed. I am tracking vegetable variety dates too. I don't often look at their website since they don't ship seeds to Canada.

This past year I was able to buy a copy of the 1947 Burpee catalog - and I see they haven't posted that one yet, if they ever intend to. It's the only new "oldie" I've acquired lately.