>>>SYS(2015) is not safe either, SUBSTR(SYS(2015)3) is safe AFAIK.
>>
>>Why?
>
>Because the help says so <g>
>
>SYS(3) may return a non-unique name when issued successionally on a fast computer. Use SUBSTR(SYS(2015), 3, 10) to create unique, legal eight character file name.

No, help doesn't say that SUBSTR(SYS(2015)3) is safer than SYS(2015) itself.