I recently did a MR just for the fun of flying and to get MQM on Delta.

MCI-ATL-BWI-JFK-LAX-ATL-MCI all on Delta. It took 26 hours.

I was not able to print my boarding passes at home because of some obscure reason. The kiosk at MCI would not print the boarding passes out either. The ticketing agent was only able to print passes for MCI-ATL, ATL-BWI, BWI-JFK, He said he was unable to print the others because of some 6 hour thing.

Does anyone know why they can't check you in and print out all the passes for travel in the same 24 hours?

It was not fun getting checked in at JFK with the GA questioning the validity of my routings in the same day. I said hey, I booked it on Delta.com. Finally a woman dressed in bright red came over and gave me my remaining boarding passes.

What, if anything, should I have done differently?

As long as you remained calm and explained that you booked on Delta.com, I think you did all that was required. I did a 28 hour MR this week on UA/US and had similar problems in printing out BPs but never had any issues at the gates and even got a free upgrade to E+ and was able to use a certificate to get to F on one leg.

I did one recently on CO and had some trouble too. I flew SMF-IAH-PHL-IAH-SMF and was only able to check in for the first two flights and print boarding passes at 24 hours prior to departure. It didn't even let me check in for the last two flights at the same time.

I thought 'no big deal, I'll just get them at the airport when I start my MR). The lady at the check in counter said that she could only check me in and print boarding passes 4 hours prior to departure, which was bad because I didn't have much time for my connection in PHL.

I ended up being able to check-in online (free wifi at SMF ^) then asked the gate agent to print the boarding passes for me.

So it took a combination of online check-in and GA assistance for me to start my MR with all the boarding passes.