Learn English – “at an early development stage” OR “at an early stage of development”

Let me self-answer with final product. Even though the solution may not be a product, the phrase best describes the iterative and evolving process.

"Training" and prepositions.

https://en.oxforddictionaries.com/definition/train starting from here, and http://www.oxfordlearnersdictionaries.com/definition/english/train_2 here:

• to train for - To archive something. "To train for your first ride", "To train for promotion"

• to train to - In order to do; to able to do. "They trained them to run very fast"

• to train to be - To be able to be. "He trained to be stronger"

• to train in - To be better in something. "She trained in pediatrics", "I don't have any training in interior decorating"

• to train as - To be taught through sustained practice and instruction. "He trained as a plumber" (http://sentence.yourdictionary.com/training)

• to train on - To educate someone in the use of something. "We trained him on the high diving board" (http://idioms.thefreedictionary.com/train+on)

• to train about - *Rare find. "Teaching doctors in training about management and leadership" (http://www.bmj.com/content/343/bmj.d5672), "Get training about how to use GIS" (http://www.in.gov/gis/2350.htm).

• [transitive] Train something (around/along/up, etc.) to make a plant grow in a particular direction. "Roses had been trained around the door"