Should one be hybridizing with a first year seedling? Kristine Albrecht shows she is willing to when the flower is special enough. https://youtu.be/votm5-xp5tk?si=Xr_ssLvepjAirUT4
Hybridizing Dahlias
There is a big difference between using a really good first year seedling for hand pollination where you select an excellent pollen parent and just saving seeds from a bee pollinated plant. The bees seem to be confused about what pollen to use.
I am in the process of collecting seeds after a batch of wet weather. The seed pods are not ripe and I have been marking the juicy looking ones with flagging tape to harvest later. There will be a nice harvest of seeds but it will take the week or so of dry weather to ripen them. Oops, there are only 4 days scheduled of dry weather. 
I found some seedpods that needed to come off the plants. I can forget so easily what I pick, so came up with something that others might want to occasionally use. Using an ultra fine Sharpie, write an abbreviation or name on the stem.
I buy masking tape at the Dollar store and write on it. I wrap it around several pods and sometimes get so many I need a rubber band. Clearview Jonas is a very nice flower and a crowd favorite at the Swan Island trial garden where it replaced a virus infected entry.
Bessie
I like the sharpie/stem idea.
On the masking tape I can write: "Hollyhill Black Beauty grown by HH Peachy Keen". There is plenty of room to write this and I can read it without glasses. I write it just once even if there are 10 pods.
Teddahlia noting what's growing nearby colected seed is important info. For the past two years I have produced a map with the location of every dahlia in my garden. However, with multiple growing locations of a given variety, I think i should start keeping tract of the location in the garden the seed is collected from. Thanks for the tip Ted.
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Cosey don't give up hope getting seed from Rock Run Ashley! I just picked 14 "seed pods" and two of the pods had seeds( 5 + 13) for a total of 18 seeds. Twelve of the seeds feel very firm. No clue if they will germinate. 
The list of possible pollen parents* is really long. If I was betting, I'd bet on Hollyhill Regal as a majority contributor pollen parent. Most every day I manually move pollen to various receptive stigmas.
- Hollyhill Regal, Sweet Nathalie, Snoho Sonia, Peaches and Cream, Marionberry Milkshake, Crighton Honey, Heather Feather, etc.
Some flowers were bred better that others. If a variety came from a long line of flowers of the same form, it will pass on more good genes to seedlings. The "one hit wonders" that were just chance seedlings but look good have little to pass on genetically. I am down on Peaches and Cream as a seed parent.
No, I am going by what has been posted of pictures of it's seedlings. It is a reasonably old variety(1993) and I would think we would know by now if it is a good seed parent. You would also be breeding to a poor maker/keeper.
Bessie I was out checking today and took another hard look at my RRA row. Still nothing. I see a big difference in seed productions over the last 7 days. I haven't checked in a week (watched pot and all) and too my delight my tried and true seed makers finally have seed pods. No frost expected in the next 10 days. Crossing my fingers!
Re: hybridizing for white.
I have an unproven theory on how to increase the odds of getting a white flower from a cross. If a Dahlia has been a stable sport to white ( e.g. White Onesta), then it's genetic color code becomes dominant, or to use computer jargon, the color is "null". I think my white waterlily 23061 may have had the pollen parent of White Onesta. Another example: The Alloway Candy plant I have is almost white ( not quite a full sport to pure white), and I observed several of its seedlings were pure white. As I listen to @Teddahlia say how rare it is to breed white Dahlias, I came up with a possible explanation of how I could have so many white seedlings.
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I think I remember Ted saying he was going to publish a guide to dahlia color genetics that would explain the intricacies of breeding white dahlias. I must have missed the release of his article, but am looking forward to reading it. 
For those of you far more experienced in dahlia seeds: do you bother saving the medium grayish black ones? I jumped the gun a bit on this seedpod. 
Color article: It is way too complicated to do easily and I am not a chemist although my son is one. He does not like dahlias particularly and would only be able answer some of my feeble questions about the terminology.
The white color color in dahlias is a breakdown of the mechanism to get the anthocyanin to form. Virginia Walbot of Stanford says there are numerous chemical steps to get the anthocyanin formed and if any of the steps fail the flower remains white. And there are numerous versions of the white because of this . Was it white because step 2 failed or was it step 6 that failed? If you cross a step 2 failure with a step 6 failure , the flower may well be red as the gene that prevented the formation of step 2 was provided by the step 6 flower. All of this makes perfect sense to me but it is very hard to write about it so you understand it.
Seeds that are sort of immature just sprout at a lower rate. Anything that germinates is a success.