Question regarding exchanging territory cards in Risk
As per the rules (1993 standard Risk) on page 7 (emphasis mine):

You are trying to collect sets of 3 cards in any of the following combinations:

3 cards of same design (Infantry, Cavalry, or Artillery)
1 each of 3 designs
any 2 plus a “wild” card


This is verified in the rules you posted:

A set is made up of 3 cards with the same Insignia..., OR 3 cards with one of each of the 3 Insignia...

In the case where you have &quot;Infantry, Infantry, Artillery, Artillery, Cavalry,&quot; you will trade in &quot;Infantry, Artillery, Cavalry&quot; as a set.