Within the 1/2/3 txt files are the commands the "UBB.threads Style Importer" uses to create the row in your UBB.threads database
Each time you import or edit the style within your Control Panel, a CSS file is generated with the name of the style, followed by the epoch date (aka, Unix Timestamp).http://www.epochconverter.com/
By looking only at the file name you mentioned above, "ubbthreads_stock_144788913," I see that within your database it is called "ubbthreads_stock" and it was created on "Tue, 24 Nov 2015 19:49:35 GMT" (and that you had upgraded your UBB.threads from 7.5.x to 7.5.9)
Every time you edit your Style within the CP, the old file is deleted, and a new one is created, with new numbers.
edited to add:
If you upgraded your site from 758 or before, your style would be called "ubbthreads_stock"
If you did a fresh install of 759, your style would be called "ubbthreads-light"
"ubbthreads_stock" = "ubbthreads-light"
The name was updated from "stock" to "light" in UBB.threads 7.5.9. Other than the name difference, they are the same.