Are Japanese maples self fertile? If so, they would have to be artificially pollinated and then bagged to avoid contamination from another parent. That's some exact timing and a lot of work. What do the seed companies say about their methods of acquiring Japanese maple seeds?
Otherwise I don't think the seedlings will be true to the named variety they came from. They will probably have the characteristics more so of one parent over the other, but not be true to the named variety you ordered. Unless self fertile, it takes two parents to make a seed.
Most of my Japanese maples are grown from seed and are almost worthless on the open market. Collectors and most customers want named varieties. Since I'm not selling them I don't care. I'm selecting the seedlings for my satisfaction, that's all. I'm on the third generation of selecting Japanese Maples that I like. The rest, after trials, get discarded.
Mike

Here is a link that might be useful: My Garden

I have no expectations of them comng true.

So far, all the nigrums have sprouted radicles...in the fridge. They got far enough along that i am growing them under grow lights.

The japonicums and shirasawanums show no sign of life yet, but three of the palmatums now have the slightest bit of emerging radicles!

I have read from one grower that he has more success with Japonicums in their 2nd year of stratification.Might be true of Shirasawanums too....worth looking into :)

I have Japanese maples popping up all over my yard. I have three good little trees in pots. Is this the incorrect way to grow them? They look good to me. Is grafting a better way to start a tree?

Kumakitty, seeds are easier to get a lot of Japanese Maples, but none can have a commercial name because a seed is not true to it's parent.
Japanese Maples pop up all over my garden also. I rescue them and grow them on. Sometimes I grow them in flats from maples I particularly like. All done outside in a protected area. I don't have all the stratification issues and bother of growing them indoors. A lot can go wrong inside. I'm not home all the time, etc.
Grafting takes time, materials, preparation and knowledge. Plus you have to grow the understock. That's why grafted plants are more expensive than plants grown from seed.
If I remember right, from my working with a Japanese landscape crew years ago, kuma is bear in Japanese.
Mike

Most JM seedlings make perfectly nice trees, although maybe not unique enough to be considered worthy of its own cultivar name and propagation.

ive only been growing J'Ms for two years now but the first time round i stratified alot of seeds i bought off ebay. I only got 9 out of 110 different seeds i used. Last September being a landscape gardener i see alot of J'Ms in customers gardens, so collected over 400 seeds this time round. i put half outdoor half indoor. Still no sign of the ones outdoor but im getting around 10/15 a week from the fridge. and on a better note i can see some of my 1st lot of seedlings from 2012's ebay seeds coming true now too.

Here's a Coral Bark maple seedling I'm growing from a few days ago. Looks pretty good to me.
Mike

Here is a link that might be useful: Fall color in my garden

Still nothing on the A. s. or A. j, but about 50% of the palmatums now have small radicles just poking. None have grown past 1/8", so I'm hoping they will advance slowly enough that I can wait to plant outdoors in a few weeks...I don't have any more room under the grow lights.

By late March or around April 1, we're normally getting warm enough that buds on most Acers already in existence are starting to swell, so I'd think that (with some frost protection) I could get them growing outdoors around that time...but tonight's predicted low of 0 isn't making that look too promising.

Question on the Acer nigrums...one is now pushing a second flush of growth. The second flush (after the cotyledons and the first two true leaves) has leaves that look MUCH more maple like. However, only the one tree is doing this...the others have a small terminal bud but no growth. Is that new flush not a normal occurrence, or is it normal that they will push the next flush, but not necessarily at the same time?

Shirasawanums now popping radicles.