The answer is there in the second paragraph of the link in Bryce's post:

"For deaths on or after September 11, 2001, Public Laws 107-103 and 107-330 made government markers available for use on veterans’ graves that were already marked with privately furnished headstones or markers. Previous law prevented VA from furnishing markers when a grave was already marked."

There have been a couple of government markers placed recently at Topeka Cemetery where only family markers had existed. And replacements are possible for government markers that are now unreadable or damaged, although that doesn't sound like the case here.