Why didn't you just buy a full size keyboard?

As far as what send numberpad scancodes versus number row I'd say it's going to be a guessing game at best.

Also for your next keyboard might I recommend a Leopold FC980 model? best of both worlds.

I'm happily rocking a 65% + trackball + numberpad combo with the trackball situated in between the other 2.  Lets me keep my trackball closer for most of my work (as I use it far more than the number pad), but I have full functionality if I need to do data entry.  I'd never go back to a full sized keyboard myself.  For the numberpad, I'm using an old variety Leopold 210TP with the number row scan codes, but as I just use it for entering numbers and not macros, it works perfectly fine for that.  Excellent build quality.

I've also heard good things about the Varmilo VA21M / VA22M.  It's available at a few places, including Massdrop at times.  You can also get one by emailing their rep Cynthia and dealing with Varmilo directly.  There's some info in the Vendor Forums.  Also a longer thread on reddit.

https://geekhack.org/index.php?topic=85232.0
https://www.reddit.com/r/MechanicalKeyboards/comments/57rohx/varmilo_va22m/

it's the older models that were sending the correct codes then?

I think you were right the first time.  The original production run of Leopold 210TP produced the same scan codes as the numbers keys above the alpha keys on a typical keyboard.  (I have one that was purchased in the fall of 2014 and I can confirm this.)  Starting a couple (?) of years ago, there were rumours that there was now a different version in production that produced the same scancodes as the tenkey codes as typically found on the right side of a full size keyboard.  I haven't really been following those stories too close, but it seems to be more myth than reality.  Most threads related to it seem to revolve around people ordering 210TP, wanting the tenkey code output and venting when they don't get it.

If you for sure want the tenkey codes, I'd just stay away.  Having said that, the 210TP is a very nice numberpad and if you're just vaguely thinking you might possibly need those tenkey codes the odd time in the future, maybe you shouldn't be so quick to discount it over a futuristic maybe.

If you're just thinking of doing macros (and you're in the Windows world), hidmacros used to be able to distinguish different physical keyboards, despite the same scan codes.  It's been several years since I used hidmacros, but it worked well for me when I did.  The developer has since moved on to a new (but similar) project called LuaMacros, so I'm not really sure what the status of it all is, but it might be something to keep in mind if you really want both the 210TP and macros.

This might be good information for you, but I too USED to use a tenkey on the left, but now I use a macropad on the left. This happened after I stumbled on a Genovation ControlPad that was originally used for a POS(connected over USB), but it was no different than the consumer pads which has reprogramming software from Genovation.
This not only gave me my 10 key functionality, but it also holds a ton of extra macro keys, and can be used as a complete keyboard replacement for gaming. My particular version had MX-blacks, and I think they all do, but I would recommend a macro pad, even if you go with something else. Might as well get the most out of the extra desk clutter.