Simlar story, happier ending: I had two jobs, one of which always did its schedule two days before the other one. Once, I gave Job 2 my schedule from Job 1, and Job 2 assistant manager still scheduled me to work on a day where I was already scheduled to work at Job 1. I pointed it out to him, and he just said, "I need you that day." I said, "Well, I'll be at Job 1 that day, because they scheduled me first, so you need to replace me that day." Come the day, I go to Job 1. The manager from Job 2 called me to ask where I was. I said, "I'm at Job 1. Both jobs scheduled me to work at the same time on the same day." He asked how I picked which job should win this scheduling conflict, and I said, "This job scheduled me first." He said, "Did you tell this to [assistant manager]?" I said, "Yes, I told him both before he made the schedule and after." Manager said, "That's all I need to know, thanks." And I never heard another peep about it, and I never had another such scheduling conflict come up.

OP said they reminded the manager 2 weeks prior. I’d say that’s well within 2 months, but I could be wrong.