Luckily I have the Michigan State Bulletin of 1939 which details the history and traits of a huge number of early varieties and has been a great resource for me.
The original name was Bonny Best, not Bonnie, and this variety has nothing to do with the Bonnie plant farm.
Middleton did make that selection and it was introduced by Walter P. Stokes in 1908.
There are many synonyms for this variety b'c back then the seed competition was fierce and seed companies changed the names of varieties to indicate they had something new. I just counted 14 synonyms for Bonny Best.
And here's a wee paragraph that may make the situation clearer and pertains to Bonny Best and John Baer as we even know them today. Remember this is from 1939.
"The identification of Bonny Best. John Baer and Chalks Early Jewel is complicated by the fact that the names Bonny Best and John Baer are used interchangeably. Some of the most critical seedsmen use seed of John Baer for Bonny Best because both names are equally popular although the varieties are practicaly identical. Some seedsmen supply seed of Chalk's Early Jewel regularly for John Baer and Bonny Best."
Given that background and knowing that both Bonny Best and John Baer are both with us today there's perhaps no reason at all to know what is being grown between those two varieties.
The specific traits of Bonny Best are given and it's a very long section so I'll just make a few comments from that section.
slightly flattened globe shape
Usually weighs 5-6 oz
about 2 3/4 to 3 " transverse diameter and 2 1/4 to 2 1/2 polar diameter
radial cracks are common but circular growth cracks are rare.
Borne in clusters of of 4-7 fruits
Interior medium scarlet with 6-7 medium cells ( we call them locules now)
Finally, no one really knows, me talking now, what the selection was done for from Bonny Best that gave us John Baer and the MI State bulletin considers them to be identical.
Ah yes, the above from 1939, the year I was born,
so ASAP I know the data is 72 yo but the earlier the data is for any specific tomato variety the more accurate it usually is with respect to everything having to do with that variety. Subtle mutations, slightly crossed seed, etc, can all have an influence on a specific variety known 100 years ago or more as opposed to today. A good example are the Livingston varieties that are featured at Victory Seed with backgrounds and seeds for many of them. And many of those varieties are as they should be b'c Livingston wrote a book and described them in detail.