What is the correct last version for Snow Leopard?
 

The home page says,...but v2.7.5 seems to work fine in my Mac OS X 10.6.8. Does the home page system requirement for Snow Leopard need to be edited, or should I go back to v2.7.1?

It's no mistake. Most users should use 2.7.1.

2.7.5 uses launchd for scheduling, while 2.7.1 uses cron. launchd, in 10.6.x, is unreliable on enough systems that I think users are better off using cron. (The changes in later versions primarily focus on compatibility with later OS differences and peculiarities.)

If you're finding 2.7.5's scheduling isn't unreliable on your 10.6x system, you can continue to use it if you want...but in general, 2.7.1 is what users should install.

Understood. I didn't know that, and will bear it in mind. Thanks for the clear & concise reply.

I do have two friends I put onto SuperDuper! whose nightly schedulings under 2.7.5 have run without incident on their Snow Leopard Macs for for a long time. Maybe they've just been lucky.

I googled around for reports on when launchd may be unreliable on Snow Leopard, and I found this on MacTech: MacEnterprise: Snow Leopard, launchd, and Lunch

Thanks again for the heads-up, David!

It's definitely not a super common issue, but it was a problem on some systems, and given the nature of the changes that were relevant to 10.6.8, it was prudent to provide a version with the broadest 10.6.8 compatibility.