Hi Radu,
You should be aware that ISPs do not start directly as big companies. Some small local ISPs do not consider to be a good "investment" to become LIR from day 0, so they don't. They start with a small *assignment* (not very often a sub-allocation) from the upstream provider
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Weather this situation should be treated in the document - not sure. However having a mention that this is not how things are supposed to happen would be a good idea.
I think this would indeed be a good place to recommend against this, but maybe the other way around: "When providing address space to a smaller ISP you should give them a sub-allocation (not an assignment) that allows them to make properly sized (see the rest of this BCOP) assignments to their customers." or something like that. Cheers! Sander