Estimation becomes a lot easier a few weeks into any project. Once you have the framework and an overall story down, and you start getting your hands dirty with a few classes, the estimation numbers start to have more confidence and weight.
The only thing you can really confirm though, is what is already completed, and that is what you should keep the stakeholders posted on. And a description of work left, not necessarily the time it will take.
I don't understand, why not just be fully transparent?
This is the work left, we think it's this size*, this is how much work we've been getting done. It looks like we might be done at this date but that's dependent on a) our estimation being correct and b) our pace continuing.
I think it's more about managing expectations than it is about managing the information you let stakeholders have.
The only thing you can really confirm though, is what is already completed, and that is what you should keep the stakeholders posted on. And a description of work left, not necessarily the time it will take.