It wouldn't make sense to add new weapons. How many weapons were developed between yesterday and today, how many entered service in the army between yesterday and today? Exactly.
That's the amount of time between HL2 and the episodes. Each picks up where the other ends.
"Hey guys, can you complain about my gamertag? I want to change it to Chingy-XXXXXXXXXXXXXXXXXXXXXXXXX"
... I'm just saying.
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