The band didn’t like my mixes until…

The curse that keeps on giving. Cliff meet lemmings.....

Although your instincts were pretty good in doing this, you should approach normalizing with some caution. Normalizing isn't the same as having a common loudness.  It may work reasonably well if the instrumentation is the same throughout an album.  But if something in the instrumentation is different, then you might still have the problem of some tracks being perceived as louder than others. Using a more up-to-date metric (like Integrated LUFS) is a more dependable way of making an album hold together in terms of level. This moves you a little into the realm of mastering and it's clear your clients didn't understand it when you told them it wasn't mastered. I expect that's not uncommon.

And at the risk of sounding like the grumpy old schoolteacher (I had a few of those back in the day), make sure not to normalize to 0dBFS.  Leave yourself a dB or two below full scale and you'll avoid overshoot when the files are run through a mux like MP3.