One thing I noted that's unclear - the XSD says that currency is always fixed to EUR (euro). Other documentation says that all local tax authorities agreed to accept this format.
This makes no sense, as my local regulations (UK) require me to report VAT in GBP. So, the SAF-MOSS XML specification, which apparently the local tax authority will accept, appears to contradict local tax law. Perhaps they meant to say "your local reporting currency" instead of "fixed to EUR". Who knows? I'm not sure even they do.
(And if I have to specify in EUR, then that means that when a Polish buyer buys using his USD PayPal balance, then presumably I have to track this in all of GBP, EUR, USD and Zlotys...)
In my view, it'd be foolish to try to find a harmonisation of every jot and tittle of these contradictory regulations. We should make a best-effort attempt, based on the local guidance from the authorities in our jurisdiction. The contradictions will become clearer to the various tax offices, and then hopefully they will issue official guidance, which we can follow - rather than waste our time engineering things which we then have no use for, later. In the UK, the HMRC has said that they're going to apply a light regulatory touch at first, as people struggle with the implementation challenges - and I suspect that also means, "as HMRC try to work out a lot of issues themselves".
David
