Didn't the 1987 Constitution state that Tagalog is our national language?

There is no constitutional basis that Filipino is the same as Tagalog. The constitution simply states that "as Filipino evolves, it shall be further developed and enriched on the basis of existing Philippine and other languages"; it never defined what the Filipino language is.

There is, however, a discrepancy of what is written in the Constitution and what is actually happening. Despite of the Constitution stating nothing whether Tagalog and Filipino are the same, the language being taught in the schools now in the Philippines can be classed as dialects of the Tagalog language.