I use 7/32 files on my 3/8 stihl chains all the time. I'm not sure that I have any 13/64 files?
Been hand filing since 1973, started using Stihlsaws in the 1980s. Back then Carlton chains were the most bang for the buck and I had plenty of 7/32 files.
The Stihl chains didn't seem to care. I'm using all Stihl chains now. Others may beg to differ?