Lots of questions .... Is there a reason you are using Oasis? And are you using the Oasis growing medium or trying to use the ordinary floral foam? There is a special product for cuttings.

And are you using new shoots from the tubers or trying to root stem cuttings? You need to be doing the former and taking a tiny sliver of the tuber with each cutting.

There is a Dahlia Forum on GW where the experts hang out. You might ask them for further advice.

Here is a link that might be useful: Dahlia Forum

Thank you for your help. For some reason I missed your reply.
I am using the oasis cubes that is meant for propagation. And, :'ve seen that method of taking a tiny sliver of the tuber but not everyone does that...at least from what I can see online. If I did have success by taking a sliver from the tuber, can I take a 2nd generation cutting from the first cutting?

Why are you doing this now? I won't even start my dahlias till late March, taking cuttings around mid April. They won't be going outside until the end of May.
I can't see any reason for starting them at this time unless you are growing them indoors under lights. And by the time they can go outside (they are short day plants and will only flower when daylight hours are on the wane) - they would be enormous.

I know you do things differently in the US - lots of indoors stuff, climate extremes and all....but growing them this early sounds like a whole world of grief and hassle to me

The easiest way would be to plant the whole tuber under forced conditions then root the first lot of shoots which will arise within a few weeks of increasing heat and light (between 3-6 weeks). This is how commercial cuttings are mostly produced. If you can maintain a good level of constant heat and light, you should be able to root around 3 separate lots of shoots (1 or 2 at a time depending on the number of growth eyes in the original tuber) before planting out the 'mother'tuber. Many growers insist that the best plants always come from rooted cuttings from a second season tuber (I honestly haven't noticed much difference myself)....Forcing a tuber into early growth is the way I always increase my stock. Even so, I won't be starting mine under glass till mid March.