What's the difference between AHEM____.TTF and ahem3.ttf ?

Hello,

http://test.csswg.org/source/fonts/ahem/
AHEM____.TTF      2014-05-30 00:04   12K

http://test.csswg.org/source/fonts/
ahem3.ttf         2014-05-30 00:04   14K

What is the adequate usage for ahem3.ttf ?

In what way is ahem3.ttf different (or better) from (than) AHEM____.TTF 
?

Gérard
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