In Macon (a couple of hours down I-75 from Atlanta) there were for a long time two Waffle Houses on either side of the interstate at the Pio Nono exit

How do you decide which one to enter?

IIRC one of them is for catering only

There's a pair off of I-85 just north of Atlanta like that (see other comments to that post), so yeah, it wouldn't surprise me. Do both of them show up on Waffle House's map? It looks like they don't put the catering-only locations there - I guess they don't want people showing up?

This sounds possible, but where is it?

A quick Kagi found a few of them, apparently a Waffle House has to be a certain size, and if they can do more business, it spawns another one.

They're on Chamblee Tucker Road right off of I-85 in NE Atlanta. Here's a screenshot from Google Maps: https://ibb.co/0tdBRR1

Now that I think about it I actually used to drive past them sometimes! Only one of them shows up on Waffle House's own map, though.

Here's an article talking about double Waffle Houses, from 2019, when the older of the two at Buford Highway / I-285 closed: https://www.tonetoatl.com/2019/07/Waffle-House-Closed-Buford... - they mention the pair on Chamblee-Tucker. Apparently one is catering-only, which probably explains why it doesn't show on the map. They also mention pairs that used to exist at Clairmont Road near I-85 and Lawrenceville Highway near I-285. Apparently WH is trying to reduce the number of these.