Yes, 1987/1988 was an incredibly productive time for U2. I remember that I could not believe how much great stuff they were putting out that year. They seemed to be a creative juggernaut.
I remember reading in an article that year that Bono said he wanted U2 to be like the Beatles in that the Beatles would put out sometimes a few records a year (all with great songs) and he wanted U2 to match it. Given the creative volume they put out that year I really thought Bono meant what he said.
I remember buying so much stuff in 87/88 and thinking that they had already beaten the Beatles as far as I was concerned. They had put out:
-Joshua Tree album
-Multiples singles from the Joshua Tree album (each with 3 or 4 "b" sides)
-Collaboration w/Robbie Robertson (Sweet Fire of Love/Testimony)
-Contribution to the "Folkways" album (Jesus Christ)
-Contribution to "A Very Special Christmas Album" (Christmas, Baby Please Come Home)
-Rattle and Hum with several excellent new songs and several singles released from it with additional new songs and covers
-there must be more, but that's what comes to mind now
-(those were also the days of scrounging through the less-reputable record stores around looking for every bootleg U2 concert recording I could find)
Those years may have been the peak of the volume of creative output for U2, but the best is always yet to come.