Maybe I'm misreading this, but how is giving July or August date ranges (fluctuating though they may be) but thinking that September delivery is a "best bet" under-promising and over-delivering? It's the exact opposite. If they really wanted to do that, they should tell all of us not to expect our cars until September and fill orders as they are able well in advance of that. Then, any surprises are to the upside (i.e. earlier than expected) rather than the downside.
Additionally, if Tesla truly is only building foreign cars right now and not building any US cars for the first weeks/month of the quarter (which I also have a hard time believing is 100% true) then giving anyone a July delivery date is a flat out lie as it's not possible to fill a US order if you won't even build a US car in July. Tesla routinely practices over-promise, under-deliver.