API-level difference between Google Checkout and Android Market documented?

Question

PREAMBLE: this question is wildly obsolete. There's no more Google Checkout and no more API.

Android Market uses Google Checkout for paid app sales. Google Checkout has a fairly extensive API. The behavior of Android Market accounts is markedly different from that documented for vanilla Google Checkout. Some examples:

• URL callbacks upon sales don't work
• Some XML API methods are not supported - e. g. <archive-order>
• In XML notifications, undocumented elements - e. g. <agent-private-data> under <shopping-cart>

Are those Android specifics documented anywhere?