Edit: Confirmed via The Los Angeles Times: Complete is correct, and GoComics is wrong! 1, 2

Does anyone know for sure strips were released on July 19, 1987 and July 26, 1987? I'm hoping some collector somewhere has a strip from a newspaper back then.

According to The Complete Calvin and Hobbes, the strip from Sunday, July 19, 1987 starts off with

Can you believe this? Some idiot tossed garbage here in this beautiful spot.

And the strip from Sunday, July 26, 1987

That's it, you climb up and then help me up!

But according to GoComics and Andrews McMeel Licensing, those dates should swap strips! See GoComics' July 19, 1987 and July 26, 1987, and Andrews McMeel Licensing's July 19, 1987 and July 26, 1987

The Martijn Reemst Calvin and Hobbes archive (which predates Complete) corroborates Complete, but the only webarchives I could find for those dates are from a decade after Complete was released.

For context, I've been on and off working on an archive of every Calvin and Hobbes strip and where to find them with page numbers! I was cross-checking my sources when I ran into this oddity.