Wow, didn't realize this would be anything but a simple question, LOL.
I DL'ed the Sparkfun library, and I believe the component package "POWER_JACK_PTH" is the generic one with the big round holes rather than the slots. I've used a gerber file viewer to verify that the "SPC4078" package I was originally looking at did define slots for the tabs. The round holes for the "POWER_JACK_PTH" package had the same diameter as those slots, so I suppose that's consistent.
Coding Badly, I saw your comment about the Adafruit library component having "holes that are way too big". Were these even bigger than the package outlines used by the Arduino boards? The Sparkfun "POWER_JACK_PTH" package looks like its holes are the same as those used on the Arduino boards (e.g., Uno, Leonardo). Which, now that you mention it, do look way big, but I suppose that's so they will adapt to fit most variants out there. Looking closely, there's a lot of solder filling those holes!
I may have to go this "generic" route anyway since I haven't even got the parts yet -- still on order. And I'd like to use an adaptable package outline so I didn't have to go back to the same supplier everytime to get more components, and hope they haven't changed supplier!