In the Law of titan Section 15 is states " ... an Angel that has already fought in another Legion in a victorious Battle this Engagement Phase may be summoned ... )
In other words you can summon a angel in every battle you have in the Engagement phase.
But in Colossus it only lets you summon an Angel once during the Engagement phase. I believe colossus is wrong in this case.
2nd last line of Paragraph 15 (just before 15.1.):
Only one Angel can be summoned by a player during his entire Engagement Phase.
I suppose the line you mention refers to angels that have fought in legions in which they had been when battle starts.
Edit 7.10: "when battle starts" ... - or was acquired in a battle, I guess.
Last edit: Clemens Katzer 2015-10-07
Closing, was a misinterpretation of rules on user side.