You are correct. It's only in the next generation, when collected seed is grown on, that crossing would make a difference. btw some of those can't cross, being different species.

What was the source of your seed?

Yes, if you got the seeds from someone who was growing kabocha, yellow crookneck, zucchini, and gourds close together, that can happen. That being said, viral infections (e.g. mosaic) and insects (e.g. aphids) can result in bumpy fruit. For viruses, one might expect the leaves to be bumpy as well. In properly moist soil, mosaic virus will only last there for a few months.

I too am curious as to what the seed source was.

There was more than one source Kitazawa and some common brands i will post a picture of the harvest.

I'd send your picture to at least Kitazawa. It's up to them to tell you what they did wrong.

Kabocha is Maxima. Crookneck and Zucs are Pepo.

Pepos can easily cross breed. Maxma CAN crossbreed with Pepo, but rarely, I believe.

Multiple seed from multiple sources, you might not be able to fault a vendor out of many if there is a fault.

When these were growing last summer, how much of them were growing out of bushy formations and how many were more on vining formations? A couple of those look like they could be very overgrown and mature crook or zuke, but most of them look like gourd variants.

Aside from avoiding Kitazawa, what can I do to avoid the same issue next year?

Why would you assume you should avoid Kitazawa? You might have had issues with other of the "some common brands" of seeds- what where the other common brands? Which seeds came from which companies?

You’re right about Kitazawa except that my squash to look to have kabocha and other Japanese squash in them. I had only a few leftover gourd seeds. The yellow crooks are likely overgrown. All were on vines.

Mosaic viruses can do weird things to squash fruit, like causing bumps/warts or causing some color change. But it appears like you mostly have gourds in that pic. I do not see any kabocha but I do see what appears to be an overgrown zucchini and possibly a yellow crookneck. Yellow crookneck do have some bumps on them naturally. The gourds pictured are Cucurbita pepo and are technically squash so the plants would look similar. If they were allowed to sprawl around and vine together one could easily think the fruit belonged to another plant.

Rodney

I thought they had a crook and a zuke in the photo too... but they say they had only vines. So without bushing habit, I'm left to doubt those two squashes that look like crook and zuke are that.

I agree with the others - most likely various gourds of some sort. What I find most interesting in that photo is the witch on a broom. How is she "suspended" like that? Or, is she REAL!?!

Maybe this picture helps.

Looks like fishing line. You can see it if you expand the picture.