Weather will certainly affect the production.

Weather, disease, pests, available nutrient depletion, etc...

Weather as in the progression of the season (declining sun angle, cooler averages, etc) or weather more like the day to day extremes?

I think I'm dealing with nutrition well, feeding regularly and I just added in a boost of phosphorus so if I see a big increase in flower activity soon I'll make sure to stay on top of that next year.

I still am not sure if it's sound advice to have two staggered crops of tomatoes because the first tappers off. The gardener who stated this practice grows in Canada, the first sungold plants were in poly grow tunnels and producing April-July and the second June through present day. Maybe he just runs out of vertical space, who knows. Does anybody know if cherry tomatoes planted in Texas or Florida will yield fruit at a pretty constant rate through their entire longer season?

Every region is going to have their particular issues. Here in E. Tn., we normally get good flowering and fruit-set from late May through mid-July. Then it usually gets so hot from the angle of the sun, that even though flowering continues - depending on the variety - fruit-set drops to almost zero. But, then, as the temperatures rise and fall from the direction our weather fronts come, fruit-set is on-and-off, with a rise sometime in August.

As an example... my main tomato harvest finished about 1 - 1 1/2 weeks ago. However, the plants set fruit again as that harvest was winding up. Now there is another crop coming on all my indeterminates. This slowed down now, and we're getting a lot of rain. My guess is that if my plants survive the fungus that will undoubtedly come with the rain, they will set again in a week or 2, and will continue to set through Sept.

So, sun inclination, and especially the combination of temp. and humidity will affect the viability of pollen. However, by this time of year, unless you are using water-soluble ferts and are applying at regular intervals, or have thought ahead and side-dressed with a granular, or slow-release option at the proper times, the initial vegetative stage, as well as the first harvest have often depleted the soil's available nutrients. It's a balance because at the same time plants are making use of available nutrients, rain is washing out what the plants can't use in time. You also have pests such as aphids sucking plant fluids and reducing vigor, and disease setting in and stressing the plant's resources and priority schedule.

Then there's water and rain... in short... it's a balancing act that rarely hits the sweet spot lol.

Edit: oh, and Florida and Texas have their own issues... mainly, and determining how deeply South they are, the 1st tomato season ends mid-summer, and doesn't really kick off again until Sept.

To assume that the plants would go on forever isn't realistic. Plants get more stretched out from growth where the new growth just isn't as productive with large fruits...kinda like the old human body.

I do set out a fall crop that has fresh vigor.

I imagine like all things it ages and production decreases. There is a difference between surviving and thriving.

Here in Southern California production will stay pretty constant but drop off as the weather cools, dampens, and the days grow short. The plant becomes rangy and growth slows. I have overwintered Sungold and it just never does close to as well the second year. When I end up tearing it out (around Christmas) there are usually some fruits still on it, but there is no point to continue based on my experience. Maybe it would be different if you grew it hydroponically, but even then I would imagine the plant starts getting rangy (meaning fewer tomatoes for the space occupied) and tomatoes don't generally respond well to pruning.

I got 2 very distinct fruit set periods on my plants this year. All were planted out on 4/23 and they set fruit until we started getting consistently in the 90s on June 8. Zero new fruit were set from June 8 until June 28 when we had a cool spell for 1 week.

I picked about 110 fruit from 5 plants from July 7 until July 21 and then only 32 from July 22 until August 12 when the second flush started to ripen. Just in the last 10 days I have picked another 109 ripe fruit with another few dozen that should ripen in the next week. The plants are setting more fruit again but those won't get very big or have time to ripen so I will pick them and use for pickled green tomatoes.