All about Sorting Images in ProSelect
There are lots of sorting options in ProSelect - this article explains what's available and how it works.
Whenever sorting by filename occurs in computers, sorting is always "alphabetic" not "numeric". Both of these produce the same result provided your file names are all the same length. That is, they should be named image_0002.jpg, image_0012.jpg etc rather than image_2.jpg and image_12.jpg (which will be sorted the opposite way). Most cameras create filenames this way and you can setup Lightroom and Bridge to rename files this way.
Alternatively, you can use a third-party utility like Better Finder Rename (for Mac) or Better File Rename (for Windows). This very clever program can rename your files in lots of different ways including sorting out incorrect numbering sequences as shown below. The list of oddly named images on the left side on the left-hand side of the list will be renamed to those shown on the right-hand side.
When importing images into ProSelect into a new ProSelect album, here's what will happen...
On Macs, images are already alphabetically sorted by OSX when you add a folder of images but not necessarily when you drag in a bunch of individually selected images from a Finder window.
To make sure that sorting happens in both circumstances, just have Preferences -> Importing Images -> Settings -> Adding Images -> Sorting: Sort by Filename selected.
On Windows, files come in a random order both ways so it's best to have the above Preferences setting always selected.
If you add additional images to a ProSelect album, sorting is automatically turned off regardless of the above Preference setting so as not to mess up any changes to the order of your images you may have already made. In this case, all newly added images will be added to the end of your existing images. These will be in order if you add a folder of images on a Mac but likely in a random otherwise.
However, you can always re-sort the images in your album back into order using Sort Images By... File Name (under the Album menu). Note: this will sort the entire album across all sets and yes/maybe/no tabs into the sort order that you select.
Other Sorting Options
There are lots of other ways to sort images in ProSelect and these are all selected from the Album Menu.
Reversing the Sort Order
When you choose one of these sort options, you can reverse the sort order by holding the Alt/Option key down when selecting the menu option. For example, if you choose to sort by Ordered images, then normally all of the ordered images will appear at the top. However, if you hold the Alt/Option key down when clicking on the menu item, then all the images that have not been ordered will appear at the top.
Hint: If you have Show Thumbnail Tags turned on (under the View menu), then it's easy to find the last of the ordered images (or unordered images) when in Thumbnail View by the small shopping cart icon in the top left corner.