IP addresses: "assigned" vs. "allocated"

Solution 1:

That's basically correct. An allocated address belongs to a pool from which it may be assigned but it hasn't yet been marked as in use. Pools are managed by various organizations like ISPs, Webhosting services, and Universities.

Keep in mind that the files you're parsing are going to be outdated the moment they're published, and that any given address may have been assigned for quite a while before it gets reported back.

Edit: It looks like the comment is correct. IP Addresses marked as assigned are managed by a sub-organization, but they may or may not actually be in use. Ranges marked as allocated should not be in use, except for where there is a lag in updating these reports. Keep in mind this comment about that data:

In particular, it should be noted that these reports seek to indicate where resources were first allocated or assigned. It is not intended that these reports be considered as an authoritative statement of the location in which any specific resource may currently be in use.

http://ftp.apnic.net/stats/apnic/