Goodman Games

Page 98
4. A caster who is last in the order cannot have his spells countered.

Then

Page 99
The spellcaster who is last in initiative order has the disadvantage of only being able to respond to spells, not initiate the spell duel.

Question: How can a caster both be unable to initiate a spell (page 98), and not have his spells countered (page 99)?

Warning, Ive literally just cracked open the book and started at page 98 so I could be missing something

I reckon that paragraph is just pointing out that the initiative-last spellcaster, if he chooses to counter-spell, enters into the duel on the opposing caster's terms. He's responding to the spell that's being cast.

He is otherwise free to take any action, such as casting another spell, as normal.

Note that's just what happens in the first round of the example duel.