Am I correct to assume this?

Yes, if you're using enough CGM to function as a pre-m, that is. Also, first-time use often doesn't seem to show the impact that third-year use will as the effect seems to build.

Also, fall planted seeds tend to sprout in fall, so you may not have an issue. If you dormant seeded (after it got too cold for them to sprout), you will have an issue.

All in all, if you dormant seeded, I'd skip the pre-m this year.